JPH01321460A - Developing device - Google Patents

Abstract

PURPOSE:To prevent the stagnation of developer by prolonging and setting the end of a base casing of a developer stirring chamber at the facing part of a developing sleeve, arranging the magnetic poles whose polarity is the same at the facing part of the developer stirring chamber of an upper developing sleeve, and providing a magnetic pole which is the same polarity as said poles or a part without magnetic pole inside of an lower developing sleeve. CONSTITUTION:The end of the base casing of the developer stirring chamber 46 provided at the side part of the developing sleeve 39 is prolonged and set at the facing part of two developing sleeves 37 and 39 which are adjoining each other and are arranged vertically. Magnetic poles N4 and N5 which are the same polarity are adjoined inside of the upper developing sleeve 39 and at the region facing to the developer stirring chamber 46. Meanwhile, a magnetic pole part whose polarity is the same as the said magnetic pole or the part without magnetic pole inside of the lower developing sleeve 37 and at the region facing to the magnetic poles N4 and N5 through the base casing 50. Thus, developer which is dropped from the developing sleeve 39 does not stagnate and is took into the developer stirring chamber 46.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is directed to electrostatic charge l) formed on the surface of an electrostatic latent image carrier using a two-component developer consisting of a toner and a carrier.
The present invention relates to a developing device that visualizes an image.

(Prior Art) Conventionally, as a developing device using a two-component developer consisting of toner and carrier, the one shown in FIG. 6.7 has been proposed.

This developing device has two parts facing the electrostatic latent image carrier (200).
It has two developing sleeves (61) and (62), which can be rotated in the directions of arrows (m) and (n), respectively.

Also, behind the developing sleeve (62) is a developer stirring chamber (
66), and the bottom casing (65) of the developer stirring section (66) is connected to its tip or to the developing sleeve (66).
It extends to the opposing parts of 1) and (62).

Furthermore, the developing sleeves (61) and (62) each have magnet bodies (63) and (64) each having a plurality of magnetic poles built therein in a fixed state independently from the developing sleeves (61) and (62), In particular, inside the developing sleeve (62), magnetic poles (Sa) and (Sb) of the same polarity are adjacent to each other in a region facing the developer stirring chamber (66). On the other hand, a magnetic pole (Na) facing the magnetic pole (Sa) is provided inside the developing sleeve (62) via the bottom casing (65).

In the developing device with the above configuration, the developer is supplied to the magnetic body (6
3), is held in a magnetic plan state on the outer periphery of the developing sleeves (61), (62) along the lines of magnetic force generated from the developing sleeves (61), (6'4), and is and is transported in the direction of the arrow. In addition, the developing sleeve (
When the developer conveyed from the developing sleeve (61) to the developing sleeve (62) reaches the opposing part of the magnetic poles (Sa) and (Sb), the outer peripheral part of the developing sleeve (62) is caused by the repulsive magnetic field formed by these magnetic poles. The developer stirring chamber (66
), where the toner and carrier are properly mixed.

The developer mixed in this way is applied to the height regulating plate (67
), the developing areas (68) and (69
) to visualize the electrostatic latent image formed on the surface of the electrostatic latent image carrier (200).

The developer that has passed through the development area (69) repeats the following two operations again.

(Problem to be Solved by the Invention) However, in the developing device, the developer stirring chamber (66
) A magnetic pole (Sa) housed in the upper developing sleeve (62) and a magnetic pole (Na) housed in the lower developing sleeve (61) face each other with the bottom casing (65) of the developer sleeve (65) in between.

Therefore, the seventh
As shown in the figure, a magnetic pole (N
The magnetic field lines between a) and (Sa) are connected to the bottom casing (6
5).

For this reason, the developer conveyed to the area (W) is restrained by the magnetic lines of force there and stays there, interfering with the developer sent later, so that the developing sleeve (62) and the bottom casing (65) However, there is a problem in that the developer becomes clogged during the development process, the transport of the developer stops, and the developer overflows to the outside of the developing device.

(Means for Solving the Problems) The present invention has been made to solve the above-mentioned problems, and will be described with reference to FIGS. 1 to 5 showing one embodiment. Developing sleeve (37), (39)
The developing sleeves are rotated in the same direction, and a circulating flow of developer surrounds these developing sleeves (indicated by flows ① to ① in Fig. 2). ] In the developing device (1) for forming the developing sleeve (
A developer stirring chamber (stirring tank) (46) is provided on the side of the developer stirring chamber (46), and the bottom casing (partition wall) of the developer stirring chamber (46)
The tip extends to a region where the two adjacent developing sleeves (37) and (39) arranged vertically are opposed to each other and conveys the developer from bottom to top, and is located above the tip of the bottom casing. The magnetic poles (N, ), (N5) of the same polarity are adjacent to each other in the area of the upper developing sleeve (39) facing the developer stirring chamber (46), while the magnetic poles (N, ), (N5) of the upper developing sleeve (39) A magnetic pole portion having the same polarity as the magnetic pole is provided inside the upper developing sleeve (37) located below in a region facing the magnetic poles (N, ), (N,) via the bottom casing (5O). Magnetic poles (N,,) shown in Figure 4.5],
Or a non-magnetic pole part [shown as (U) in Fig. 2.3. ].

(Function) According to the developing device (1), as shown in FIG. 4, the two-component developer consisting of toner and carrier has a flow of
The developing sleeve (37
), (39).

Then, at the opposing portion of the developing sleeves (37) and (39), the developer that has flowed over the developing sleeve (37) and has been transported along the direction (2) is transported to the opposing area (F) of the developing sleeve with magnetic poles (S, ) and transferred to the developing sleeve (39). Further, the developer held in the developing sleeve (39) is conveyed along the flow (2) based on the rotation of the developing sleeve (39), and the developer is transported along the flow (2) by the magnetic pole (N, ), (N 5), which separates from the surface of the developing sleeve (39) due to the repulsive magnetic field formed by the
It is conveyed along the bottom casing (50) on the flow (■).

Here, as shown in FIG. 3, inside the developing sleeve (37), the magnetic pole (N
4) is the non-magnetic pole part (U), so the lines of magnetic force formed between the magnetic pole (N4) and the non-magnetic pole part (U) are along the surface of the bottom casing (50). It is distributed in

Therefore, the developer separated from the developing sleeve (39) does not stay in the area (Z) and flows into the developer stirring chamber (46).
be taken in.

(Example) The present invention will be described below with reference to the accompanying drawings.

,＜, , , , ,Structure of the image device 1. .

[B] Schematic Structure FIG. 1 shows a developing device (1) according to the present invention, and this developing device (1) is generally composed of a toner replenishing device (2) and a developing device (3).

[ii] Toner replenishment device (2) The toner replenishment device (2) includes a cartridge storage section,
A toner cartridge (15) is installed in (4).

The cartridge accommodating portion (4) has a rear wall (7), a supporting member (6a), ( 6b), (6C
) is passed over the rack, and a substantially semicircular bottom plate (9) is supported by the supporting members (6a), . . . , (6c). In addition, the bottom plate (9)
is, the tip thereof is locked to the arm part (l l), and the arm part (l l) is attached to the side plates (5), (5) with the shafts (10), (1
It is rotatably attached via 0). In addition, the bottom plate (
One end of a spring (12) is locked to the bottom of the spring (12) and biased in the direction of the arrow (a). When the toner cartridge (15) is not installed, the biasing force of the spring (12) causes the spring (12) to move in the direction of the arrow (a). It moves in the direction a) to close the toner replenishment port (27) of the developer 1tK3), which will be described later.

The toner cartridge (15) has a stirring blade (18) inside a cylindrical body (16) with both ends closed through a support shaft (17).
The main body (16) has an opening (19) formed along the axial direction.

The toner cartridge (15) has side plates (5), (5)
), the support shaft (17) is lowered along the guide portions (13), (13) formed in Mouth (2
7).

When the toner cartridge (15) is installed, the bottom plate (9)
) moves in the direction of arrow (a') about the shaft (10) against the biasing force of the spring (12), and the toner supply port (27) is opened.

Note that the toner cartridge (15) is prevented from falling off by a lock portion (8) provided on the rear wall (7).

Furthermore, when the toner cartridge (15) is installed, the handle (47) located in the cartridge accommodating portion (4) is rotated in the direction of arrow (h) and placed out of the way.

[iii] Developing device (3) The developing device (3) is roughly composed of a toner supply section (20), a developing section (35), and a developer stirring section (45).

(B) Toner supply section (20) The toner supply section (20) receives the toner supplied to the developing device (2) from the toner cartridge (15) of the toner supply device (2), and transfers it to the developing section (20). 35).

In the toner supply section (20), between the bottom frame (21) constituting the developing device (3) and the partition walls (49) and (50) that partition the developer stirring section (45), A toner supply roller (22) is arranged at the front, and a toner hopper (25) having a stirring blade (26) is formed at the rear.

The toner supply roller (22) has minute irregularities formed on its outer circumference, and partition walls (
50), the blade (2) attached to the bottom frame (21)
3) The tips of the toner outflow prevention plates (24) are pressed into contact with each other.

Note that the toner supply roller (22) is connected to an AC power source (31).
) and the recovery bias voltage (■5) from the DC power supply (32) (
-Vrms+Vss) is applied.

The toner hopper (25) has a slope (28) going diagonally upward.
is connected to the toner supply port (27) via the ramp (
28) is rotatably provided with a toner empty detection device (30). In addition, a toner spill prevention sheet (29) is attached to the lower edge of the toner supply port (27).
The tip contacts the outer periphery of the toner cartridge (15) to prevent toner from spilling out from the gap between the developing device (3) and the toner cartridge (15).

(b) Developing section (35) The developing section (35) receives and takes the toner supplied from the toner supply section (20), and while conveying the toner and carrier, it passes through the photosensitive drum (100), which is an electrostatic latent image carrier. ) toner is supplied to the electrostatic latent image formed on the surface of the image.

In the developing section (35), the space formed between the bottom frame (21) and the sleeve cover (36) includes a developing sleeve (37) at the bottom and another developing sleeve (39) at the top.
), the lower developing sleeve (37) faces the toner supply roller (22) with a predetermined minute gap, and the upper developing sleeve (39) has a sleeve cover (36) on the top. The height regulation plate attached to the rear (
The tips of 41) are opposed to each other with a predetermined height regulating gap.

In addition, the developing sleeves (37) and (39) are connected to a DC power source (4).
2), development bias voltage (V b 1) from (43),
(V b J is applied to each. Furthermore, the developing sleeves (37) and (39) are
Magnet bodies (38), (40) independently from (37), (39)
) is housed in a fixed state.

The magnet body (38) has magnetic poles (N,), (Nt), (s
υ, (N2), and the magnetic pole (N1) is connected to the photoreceptor drum (1
00), the magnetic pole (N,) is the toner supply roller (
22), and the magnetic poles (S,), (S
, ) are respectively between the magnetic poles (N1) and (N, ),
The magnetic pole (S,) is located on the right side in the figure with respect to the opposing area (F) of the developing sleeves (37) and (39), and the magnetic pole (S,) is located below the magnetic pole (N2). (N2) should be a little wider.

The other magnet body (40) has magnetic poles (N3), ~, (N
5).

(S 3), (S , ), the magnetic pole (N3) faces the photoreceptor drum (100), and the magnetic pole (N4) and (N,
) is adjacent to and faces the developer stirring section (45).

In addition, the magnetic pole (N3) is arranged on the left side in the figure with respect to the opposing region (F), and the magnetic pole (N4) is located between the magnetic poles (N5) and (N, ) at the opposing part of the height regulating plate (41). In contrast, it is placed on the right side in the figure.

The insides of the developing sleeves (37) and (39) that face the magnetic poles (S3) and (S2) are non-magnetic pole parts (X) and (Y), respectively.

By arranging the magnetic poles as described above, lines of magnetic force are generated around the developing sleeves (37) and (39) as shown in FIG. 3.

Here, a portion inside the developing sleeve (37) that faces the magnetic pole (N4) of the developing sleeve (39) via the partition wall (50) is a non-magnetic pole portion (U);
50), where the magnetic poles (N4) face each other at the top of the tip.
The lines of magnetic force are formed substantially parallel to the partition wall (50).

(c) Developer stirring section (45) The developer stirring section (45) mixes the toner supplied from the toner supply section (20) to the developing section (35) with the developer whose toner concentration has decreased. The developer is raised to a predetermined concentration and a developer suitable for development is prepared.

In the developer stirring section (45), a stirring tank (46) is formed behind the developing sleeve (39), with an upper frame (47) at the top and partition walls (49) and (5) at the back and bottom.
A packet roller (51) is housed therein, and the front part of the partition wall (50) is covered with a developing sleeve (3).
7) and (39) are opposed to each other.

In addition, the stirring tank (46) is equipped with a lid (4) of the upper frame (47).
8) is opened and a starter containing toner and carrier mixed in a predetermined ratio is loaded.

Further, a two-component developer containing a mixture of toner and carrier is held on the outer periphery of the developing sleeves (37) and (39).

! ! , , , , , Disaster Image, Turnip, Oki, and 1 work of Ministry of Honor.

When the developing device (1) having the above configuration is installed in an image forming apparatus such as a copying machine, a stirring blade (18) is attached to the developing device (1).

(26), toner supply roller (22), developing sleeve (
37), (39), and a bucket roller (51) are each drivingly connected to a drive system (not shown).

When the developing device (1) starts driving, the stirring blade (18) moves in the direction of the arrow (b) in the toner cartridge (15).
The toner rotates in the direction of the opening (
19), the toner is fed into the ramp (28) via the toner supply port (27).

The toner sent to the toner hopper (25) is transported by a stirring blade (
26) is mixed and conveyed forward while being mixed based on the rotation in the direction of arrow (d), and is held on the surface of the toner supply roller (22) in the area (A) near the outer circumference of the back surface of the toner supply roller (22). Based on the rotation, it is transported in the direction of arrow (C), and the amount of transport is regulated at the portion facing the blade (23). The toner scraped off from the outer periphery of the toner supply roller (22) by the tip contact portion of the blade (23) stays in the toner hopper (25). On the other hand, the blade (2
The toner that has passed through the tip contact part of 3) is transferred to the developing sleeve (
37) and the toner supply roller (22) are conveyed to the toner supply area (B) where they face each other, and here the developing sleeve (37)
) scraping action of the carrier and developer being conveyed in a magnetic brush state based on the rotation in the direction of arrow (e);
Development bias voltage (vb+) and recovery bias voltage (Vs
5) (=V rms + Vs s).

In addition, in the toner supply area (B), in parallel with the toner supply operation, an operation is performed to collect excess toner on the developing sleeve (37) to the toner supply roller (22) by the electrostatic attraction force, and the developing sleeve (37) The toner concentration of the developer held above (the content ratio of toner to carrier) is maintained at a predetermined value.

Further, the toner collected by the toner supply roller (22) is conveyed in the direction of arrow (c), and the toner is transported to the toner outflow prevention plate (24).
) and are collected in the toner hopper (25).

The toner supplied to the surface of the developing sleeve (37) is taken into the developer held in a magnetic brush state along the magnetic lines of force shown in FIG. 3, and as shown in FIG. The developer and toner are transported in the direction of arrow (e) along the flow of the developer based on the rotation of the developing sleeve (37) and the magnetic body (38).
) are mixed microscopically based on the magnetic force of the two to improve their respective potentials.

The developer flowed on the developing sleeve (37) and was conveyed along the line (2). When it reaches the part facing the developing sleeve (39), it flows along the lines of magnetic force generated from the magnetic pole (S3) of the developing sleeve (39). It is attracted by the magnetic pole (S3) and transferred onto the developing sleeve (39).

As explained earlier, the region (X) of the developing sleeve (37) facing the magnetic pole (S3) is a non-magnetic pole part, and there is a region between the developing sleeves (37) and (39).
Since a repulsive magnetic field is formed between the magnetic poles (S,) and (S3), developer does not enter between the developing sleeves (37) and (39), and all of the developer is removed from the upper developing sleeve (3).
9).

Note that the developer conveyed from the direction of arrow (e) along the developing sleeve (37) is
39), the developer suddenly changes direction and heads in the direction of the arrow (f), so the developer is mixed and stirred properly here.

The developer transferred to the developing sleeve (39) is conveyed in the direction of the arrow (f) along the flow ■ based on the rotation of the developing sleeve (39), and is formed between the magnetic poles (N4) and (N, ). The non-magnetic pole part (C) separated from the outer peripheral part of the developing sleeve (39) is collected in the stirring tank (46), and the partition wall (5
0) along the flow ■ along the packet roller (5
1).

Here, inside the developing sleeve (37), the magnetic pole (
The part facing N4) via the partition wall (50) is a non-magnetic pole part (IJ), and the part that faces the magnetic pole (N4) and the non-magnetic pole part (U)
The lines of magnetic force formed between the partition wall (50) and the partition wall (50) do not intersect with each other, but are distributed approximately parallel to the partition wall (50).

Therefore, the developer separated from the surface of the developing sleeve (39) at the non-magnetic pole portion (C) does not stay in the upper region (Z) of the tip of the partition wall (50), and is quickly transferred to the partition wall (50).
is taken into the stirring tank (46) along the upper surface of the stirring tank (46).

The developer taken into the stirring tank (46) is conveyed in the direction of arrow (g) based on the rotation of the bucket roller (51), and the toner and carrier are macroscopically mixed and stirred while being circulated.

The developer being mixed and stirred in the stirring tank (46) flows ■
is conveyed toward the developing sleeve (39) along the direction of the developing sleeve (39), and a part of the developing sleeve (39)
) and is conveyed in the direction of arrow (f), and the amount of conveyance is regulated at the portion facing the height regulating plate (41).

The developer that has passed through the part facing the height regulation tf (41) is conveyed in the direction of the arrow (f) in a magnetic plan state, and is transferred to the photoreceptor drum (100) and the developing sleeve (37) facing each other along the flow (■). In area (D), photoreceptor drum (100)
The electrostatic latent image formed on the outer peripheral surface of the toner is rubbed and visualized as a toner image.

The developer that has passed through the development area (D) is transferred to the development sleeve (
39) is further conveyed in the direction of arrow (f), and at the part facing the developing sleeve (37), the flow ■
along the magnetic pole (St) of the magnet body (34) and is transferred to the developing sleeve (37).

In addition, the developing sleeves (37) to (39) explained earlier
Similarly to the transfer operation of the developer to the magnetic pole (
Since a repulsive magnetic field is formed between S, ) and (S3), the developer transfer operation here is performed smoothly.
Developer does not enter between the developing sleeves (37) and (39).

The developer transferred to the surface of the developing sleeve (37) is conveyed in the direction of arrow (e) based on its rotation, and is transported to the developing area (
In step E), the toner comes into contact with the electrostatic latent image on the photoreceptor drum (100) again, and toner is again supplied to the toner image developed in the development area (D). Therefore, toner is replenished even in areas where toner supply was insufficient in the developing area (D), and l
There will be no unevenness in agricultural yields or white spots due to insufficient toner supply.

Note that the development in the development areas (D) and (E) is performed using the development bias voltage (V b t) + (V bυ applied to the development sleeves (39) and (37) and the photoreceptor drum (10
This is done based on the potential difference with the surface potential of 0).

The developer that has passed through the development area (E) is conveyed along flow (2) to a portion facing the toner supply roller (22), where an amount of toner corresponding to the amount consumed by development is supplied.

The supplied toner is conveyed along the outer peripheral surfaces of the developing sleeves (37) and (39) as described above.

By repeating the development process as described above, the toner in the toner cartridge (15) is gradually consumed, and as a result, the toner hopper (25) and the f-circuit (
28) When the amount of toner in the toner cartridge decreases, the toner empty detection device (30) rotates in the direction of arrow (i) to detect that the toner cartridge (15) should be replaced, that is, the toner empty state. be done.

Then, by installing a new toner cartridge (15) containing sufficient toner, the toner empty state is resolved.

1! ,,,,,,JI! ! In the above explanation, the inside of the developing sleeve (37) and the magnetic pole (N4
) and the part facing each other via the partition wall (50) is the non-magnetic pole part (
U), but the magnetic poles are not limited to this, and the magnetic poles may be arranged as shown in FIG.

That is, the magnetic body (38) of the developing sleeve (37) has magnetic poles (S,,), ~, (3,3), (N,,), ~, on the outer periphery.
(N,,), and the magnetic body (40) of the developing sleeve (39) has magnetic poles (S,,), ~, (S,,), (N,,
), ~, (N, 7). Then, the magnet body (3
In 8), the magnetic poles (S, , ) are arranged in a part facing the photoreceptor drum (100), the magnetic poles (S, 2) are arranged in a part facing the supply roller (22), and the magnetic poles (S, 2) are arranged in a part facing the developing sleeve (39). The magnetic poles (S, .) and (N, .) are opposed to each other. Also,
There is a partition wall (5) between the magnetic pole (S1Z) and (S,3).
A magnetic pole (N1) is arranged at a position opposite to the magnetic pole (N1).

On the other hand, in the magnet body (40), the magnetic poles (N, , ) are opposite to the photoreceptor drum (100), and the magnetic poles (SI4) are opposite to the photosensitive drum (100).

3), the magnetic poles (N13) and (N+e) are arranged adjacent to the stirring tank (46), and the magnetic poles (S,...
) and (N, 5) is slightly wider. In addition, magnetic poles (N, 7) and (S, ,) are arranged at the part facing the height regulating plate (41) so as to sandwich the tips thereof, and the magnetic pole (
N.

A magnetic pole (S, 5) is arranged between 6) and (N, 7).

In the developing device having the above configuration, the developing device (1)
Similarly, a flow of developer is formed surrounding the developing sleeves (37), (39).

Then, from the developing sleeve (37) to the developing sleeve (39)
The developer transferred to ) is separated from the surface of the developing sleeve (39) at the non-magnetic pole part (C) formed by the magnetic poles (N, ) and (N, , ) and taken into the stirring tank (46). . Here, a repulsive magnetic field is formed between the magnetic poles (N, 5) and (N, 2), and in the upper region (Z) of the tip of the partition wall (50),
As shown in FIG. 5, magnetic lines of force are formed along the partition wall (50). Therefore, the developer is restrained in the area (Z) by the magnetic lines of force and does not stagnate.

Further, in the above embodiment, the developing device (1) was equipped with two developing sleeves (37) and (39), but the present invention is also applicable to a developing device equipped with even more developing sleeves. be.

Furthermore, in the embodiment, the developing sleeve (37).

(39) The case where the present invention is applied to a developing device that supplies toner into the flow of developer being conveyed on the surface is shown, but the toner already mixed with the carrier is supplied to the developing sleeve. The present invention is also applicable to other forms.

In the above embodiments, the case where the photoreceptor drum (100) is used as the electrostatic latent image carrier is shown, but even if the image forming apparatus uses a belt type photoreceptor, the developing apparatus to which the present invention is applied may be used. can be used.

(Effects of the Invention) As is clear from the above description, in the developing device according to the present invention, the bottom casing surface of the developer stirring chamber is extended to the opposing portion of the upper and lower developing sleeves, and the upper developing sleeve A magnetic pole of the same polarity is disposed in a portion facing the developer stirring chamber, and a magnetic pole of the same polarity as the magnetic pole of the same polarity is disposed inside the upper developing sleeve in a region opposite to the magnetic pole of the same polarity with the bottom casing interposed therebetween. A magnetic pole or non-magnetic pole portion is provided.

Therefore, at the top of the tip of the bottom casing, the lines of magnetic force are distributed along the casing surface due to the same magnetic poles, etc., and the developer separated from the upper developing sleeve does not stay there, forming a smooth circulating flow of developer. can do.

[Brief explanation of the drawing]

1 to 3 show the developing device according to the present invention, FIG. 1 is a sectional view of the developing device, FIG. 2 is a sectional view showing the flow of developer, FIG. 3 is a magnetic force distribution diagram of the magnet body, and FIG. Figures 4 and 5 show the second embodiment, Figure 4 is a sectional view showing the flow of developer, Figure 5 is a distribution diagram of magnetic lines of force in the magnet, and Figures 6 and 7 are part of a conventional developing device. FIG. 6 is a sectional view showing the flow of developer, and FIG. 7 is a magnetic force distribution diagram of the magnet body. 1... Developing device, 2... Toner replenishing device, 3... Developing device, 15... Toner cartridge, 20... Toner supply section, 35... Developing section, 37. 39... Developing sleeve , 38° 40... Magnet body, 45... Developer stirring section, 100 Photosensitive drum, N ++ ~ + N 0
% S 11~+34 Magnetic pole, x, y, c,
u: Non-magnetic pole part.

Claims (1)

[Claims] (1) In a developing device that rotates a plurality of continuously arranged developing sleeves in the same direction to form a circulating flow of developer surrounding these developing sleeves, a developer stirring chamber is provided on the side of the developing sleeves. , the bottom casing tip of the developer stirring chamber is extended to an area where two adjacent developing sleeves arranged vertically face each other and where the developer is conveyed from bottom to top; A magnetic pole of the same polarity is adjacent to a region of the upper developing sleeve located inside the upper developing sleeve and facing the developer stirring chamber, while a lower developing sleeve located below the upper developing sleeve and the bottom casing has magnetic poles of the same polarity adjacent thereto. A developing device characterized in that a magnetic pole portion having the same polarity as the magnetic pole or a non-magnetic pole portion is provided in a region facing the magnetic pole via the magnetic pole.