JPH08220885A - Developing device - Google Patents

Abstract

PURPOSE: To provide a developing device capable of freely setting the shape of a recovering container and further, suppressing a running cost as low as possible, without depending on the dispersiveness of a developer itself and obtaining a shape that the developer can be easily dispersed in a container. CONSTITUTION: In the developing device sequentially supplying the carrier developer to a developing tank 16 housing the developer consisting of toner and carriers from above, based on the signal of a toner concentration sensor in the developing tank 16, while used developer is dropped and supplied in the recovering container 35 from a developer overflowing port 23a in the sidewall part of the developing tank 16, a magnet 36 is disposed along the outside bottom part of the recovering container 35, to attract the dropped developer to the outside with the strength of magnetic force (central magnetic force < outside magnetic force). Thus, discharged developer is dispersed in the recovering container in a flat and uniform state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention develops while sequentially replenishing a magnetic developer commonly referred to as "debe" in order to visualize an electrostatic latent image on the surface of a photoconductor in an electrostatic recording device such as a copying machine. The present invention relates to a so-called devee displacement developing system developing device, and more particularly, to an improvement of an exhaust debebox or other collecting means for collecting used developer.

[0002]

2. Description of the Related Art Conventionally, in a copying machine or the like which is one of electrostatic recording devices, a developing device is arranged at a position facing a surface of a photosensitive member which moves in one direction. A magnetic developer is attached to the electrostatic latent image carried by the toner to visualize it, that is, to form a visible image. This developing device is usually one in which a developing magnet roller, a stirring screw, an agitator, and a conveying screw, which are arranged in close proximity to each other on the surface of the photoreceptor, are incorporated in a container-shaped developing tank.
A developer containing a carrier made of a magnetic material and toner is contained in the developing tank.

In this developing device, the carrier and toner are agitated by a stirring screw to triboelectrically charge the toner, and the carrier is magnetically attracted by a magnet roller to form a magnetic brush for conveyance, whereby a Coulomb force is applied to the carrier. The toner adhered by is supplied to the surface of the photoconductor, whereby the toner is attracted to the electrostatic latent image on the surface of the photoconductor, and development is performed.

In this case, during development, the magnetic permeability sensor provided inside the developing tank detects the toner concentration in the developing tank, and the developer replenishment control based on the detection signal of the toner concentration sensor develops the toner. Toner or carrier developer is replenished into the developing tank from a developer supply unit installed on the tank, and the toner concentration in the developing tank is maintained within an appropriate range.

Further, since the carrier in the developer is repeatedly used without decreasing, it is gradually deteriorated by stirring with the developing roller or stirring screw and contact with the photosensitive member. For this reason, the carrier cannot give a predetermined charge amount to the toner, resulting in deterioration of image quality. Therefore, the carrier is newly replenished in the developing tank to replace the deteriorated carrier in the developing tank, thereby suppressing the deterioration of the charging performance.

FIG. 16 shows the state of the discharged carrier developer when the carrier is replaced. In this figure, 16 is a developing tank, 19 is an agitator provided in the developing tank 16, and 23 is a developer discharging portion provided on the side wall of the developing tank 16, and overflows to the discharging portion 23. An overflow outlet 23a for discharging the used developer to the recovery container 35 is opened downward. In this developing device, the supply / discharge control for supplying the carrier developer and discharging the developer in the developing tank 16 is also performed by the control means including a microcomputer.

[0007]

By the way, conventionally, as shown in FIG. 16, the recovery container 35 is made of a box-shaped resin, and the carrier developer discharged from the developing device overflow 23a is flat and It does not enter the collecting container 35 in a uniform state, but actually, in the collecting container 35, like the sand of an hourglass, it is in a state of accumulating in a substantially conical shape with a repose angle due to the characteristics of the developer. For this reason, in the past, it was necessary to design the recovery space with a considerable margin.

That is, conventionally, the form of containing the discharged developer in the developer collecting container 35 is limited only by the nature that the magnetic developer itself is uniformly dispersed in the collecting container in a conical shape with a substantially constant angle of repose. ing. Therefore, the size of the container must be set larger than the allowable storage amount in consideration of the amount of dead space generated in the recovery container.

Therefore, there is a problem in that the installation of other mechanical devices constituting the recording apparatus is restricted in the limited internal space of the electrostatic recording apparatus. In addition, when replacing the developer recovery container, there is a problem that a replacement recovery container and a maintenance cost are required and the running cost is increased.

Incidentally, Japanese Patent Laid-Open No. 2-61671 discloses that
By changing the magnetic field applied to the magnetic powder by the operation of the rotating magnet, it is possible to supply the magnetic powder in the developing tank to the magnet roller without using stirring or a transport member, and to effectively utilize the space. A possible developing device is disclosed, but in this case, no reference is made to the developer recovery container, and since the configuration includes the rotating structure of the magnet, the leveling of the used developer in the recovery container is performed. Is virtually impossible to apply to.

The present invention has been made in view of the above problems, and does not depend on the dispersibility of the developer itself, and does not have to be shaped so that the developer can be easily dispersed in the container. An object of the present invention is to provide a developing device capable of freely setting the shape of the collection container and suppressing the running cost.

[0012]

In order to achieve the above object, in a developing device of the present invention, a developing unit for visualizing an electrostatic latent image carried on an electrostatic latent image carrier by using a magnetic developer. And a recovery container having a recovery container for accommodating the used developer discharged from the development part, in which magnetic field applying means for applying a magnetic field to the inside of the recovery container is provided in the vicinity of the outer periphery of the recovery container. There is.

More specifically, a developing tank for accommodating the developer consisting of toner and carrier is provided rotatably with a stirring means for stirring the developer and a developing roller for supplying the developer to the photosensitive member. Toner density detecting means for detecting the density of the toner in the developing tank is provided, and further, a developing method for sequentially replenishing the developing tank with a carrier developer containing toner or carrier based on a signal from the toner density detecting means. A developing device having a developer replenishing portion, a developer overflow outlet for developing agent overflow formed on a side wall portion of the developing tank, and a recovery container for accommodating the developer overflowed from the developer overflow outlet. In the above, a magnet for applying a magnetic field inside the recovery container is arranged at the outer bottom of the recovery container.

The magnetic field applying means may be disposed at the outer bottom of the recovery container, for example, the outer surface of the side wall of the recovery container, the open / close cover provided near the outside of the side wall, and the like. When the magnet is provided on the outer bottom of the recovery container, it is preferable to arrange the magnet in a U-shape so as to surround the developer overflow port. Further, a sheet-shaped magnet assembly may be used instead of the single magnet.

Further, the magnetic field applying means may use an electromagnet in addition to a normal permanent magnet. In this case, the electromagnet may be energized only when the developing device is operating, or conversely except when the developing device is operating. Always energize,
Alternatively, it is possible to energize only for a certain period of time after the end of the operation of the developing device.

[0016]

According to the above construction, since the magnetic field applying means for applying a magnetic field to the inside of the recovery container is arranged in the vicinity of the outer periphery of the recovery container for storing the overflowed developer, it overflows into the recovery container. The developer is uniformly dispersed in the container under the influence of the magnetic field. As a result, the used developer in the collection container is easily dispersed, which allows the shape of the collection container to be set freely and the running cost to be reduced.

[0017]

EXAMPLES Examples of the present invention will be described below with reference to FIGS.
It will be described based on. 1 to 5 show a first embodiment of the present invention, FIGS. 1 to 3 show a developing device of this embodiment, and FIG. 4 shows an outline of an electrophotographic copying machine in which the developing device is incorporated. FIG. 5 shows essential parts of the developer recovery section of the developing device. As shown in FIG. 4, the copying machine with the built-in apparatus of the present embodiment is basically provided with an original placing table 1 on the upper surface thereof, and an exposure optical system 2 is provided under the original placing table 1. The exposure optical system 2 includes a light source lamp 3 for scanning an original (not shown) placed on the original placing table 1 while irradiating the original, and a plurality of reflecting mirrors for guiding the reflected light from the original to the photoconductor 4. 5 and a lens unit 6 arranged in the optical path of the reflected light.

On the outer periphery of the photoconductor 4, a charger 7 for charging the surface thereof to a predetermined potential, an interimage eraser (not shown), and a developing device for developing the electrostatic latent image formed on the surface of the photoconductor 4. 8, a transfer charger 9 for transferring the toner image on the surface of the photoconductor 4 to a sheet, a cleaning device 10 for collecting the residual toner on the surface of the photoconductor 4, and a destaticizing device (not shown) are provided.

Further, a timing roller 11 for feeding a sheet at a predetermined timing is provided on the side of the sheet on which the photosensitive member 4 is inserted.
Conveying roller 12, paper feed cassette 13 and paper feed roller 1
On the other hand, a fixing device 15 for fixing the toner image transferred on the paper to the paper is provided on the paper output side of the photoconductor 4.

As shown in FIGS. 1 to 3, the developing device 8 has a container-shaped developing tank 16, and inside the developing tank 16, a developing roller 17 composed of a magnet roller and a stirring means as a stirring means. A screw 18, an agitator 19 as a stirring means, and conveying screws 20, 20 as a conveying means are rotatably arranged.

The developer contained in the developing tank 16 is composed of a carrier and a toner, and the carrier made of a magnetic material has a resin coat layer for suppressing the adhesion of the toner on the surface. This carrier and toner are mixed with a stirring screw 1.
When agitated by 8, the toner becomes triboelectrically charged. The developing roller 17 attracts the carrier by magnetic force to form a magnetic brush and conveys the carrier, whereby the toner attached to the carrier by the Coulomb force is supplied to the photoconductor 4.
It is attracted to the electrostatic latent image on the photoconductor 4 and developed.

As shown in FIG. 1, a developer replenishing opening 16a is formed on the upper wall of the developing tank 16, and the developer replenishing unit (developer replenishing section) shown in FIG. 3 is formed in the replenishing opening 16a. ) 25 is fitted from above. The inside of the developer supply unit 25 is partitioned into a toner storage chamber and a carrier developer storage chamber. One of the toner storage chambers stores toner and the other carrier developer storage chamber. Is a developer consisting of a carrier only, or a developer in which toner is mixed in a carrier in a predetermined ratio (hereinafter,
Carrier developer) is stored.

On the other hand, as shown in FIG. 1, the side wall of the developing tank 16 is provided with a developer discharge section 23 having a developer overflow 23a. The developer discharging section 23 discharges the developer overflowing from the developer overflow outlet 23a to a developer collecting container 35 described later.

At the bottom of each of the above storage chambers, a toner replenishing roller 21 driven and controlled by a controller 32 shown in FIG.
And a carrier developer replenishing roller 22 are respectively provided. When the toner replenishing roller 21 is rotationally driven, the toner in the toner storage chamber is rotated, and the carrier developer replenishing roller 22 is rotationally driven. The carrier developer in the carrier developer storage chamber is transferred to each roller 2
An amount corresponding to the driving time of Nos. 1 and 22 is supplied to the developing tank 16 through the replenishment opening 16a, and is conveyed to the stirring screw 18 side by the conveying screws 20 and 20.

Further, inside the developing tank 16, there is provided a toner density sensor 34 as a toner density detecting means for detecting the toner density in the developing tank 16. The toner concentration sensor 34 is composed of a magnetic permeability sensor, which contacts the carrier in the developer to detect the magnetic permeability, and the ratio of the toner to the carrier can be obtained from the detected magnetic permeability. For example, when the amount of carrier contacting the toner concentration sensor 34 is small, it is detected that the toner ratio is high,
If the amount of carrier that contacts the toner concentration sensor 34 is large,
It is detected that the toner ratio is low.

The detection signal of the toner concentration sensor 34 is output to the control device 32 shown in FIG. 3, and the toner replenishing roller 21 and the carrier developer replenishing roller 22 of the developer supply unit 25 are based on this detection signal. Is driven to replenish the developing tank 16 with toner or carrier developer.

Next, the copy operation in the copying machine having the above-mentioned structure will be described. Returning to FIG. 4, when a power switch (not shown) is turned on, warm-up processing is first performed. After this is completed, when the copy start switch 31 described later is turned on, the light source lamp 3 of the exposure optical system 2 scans the document placed on the document placing table 1. At this time, the reflected light from the original document is applied to the photoconductor 4 through the reflecting mirror 5 and the lens unit 6, and an electrostatic latent image is formed on the surface of the photoconductor 4 which is charged to a predetermined potential by the charging charger 7. To be done.

Next, the electrostatic latent image is developed by the toner supplied from the developing device 8. The toner image on the surface of the photoconductor 4 is transferred to the paper supplied from the paper feeding cassette 13 by the transfer charger 9, and is thermally fixed on the paper by the fixing device 15. As a result, a copy image corresponding to the original image is formed on the sheet.

Such a series of copying operations is controlled by the controller 32 which is composed of a microcomputer shown in FIG. The control device 32 is provided in the main body of the copying machine, and the ON operation signal of the copy start switch 31 is input. Further, a copy counter 33 for counting the cumulative number of copying operations is further provided, and this count value (hereinafter referred to as copy count value) n is also input to the control device 32.

When the copying operation as described above is repeated,
The toner of the developer housed in the developing tank 16 of the developing device 8 is gradually consumed, and the ratio of the toner to the carrier, that is, the toner concentration decreases. The drive control of the toner replenishing roller 21 based on the output of the toner density sensor 34 is further performed by the control device 32.

That is, when it is detected that the detection signal from the toner density sensor 34 has dropped to the lower limit value of the proper range required for development, driving of the toner replenishing roller 21 is started. As a result, the toner in the toner storage chamber of the developer supply unit 25 is replenished into the developing tank 16 and the developing tank 16
The toner density in the inside increases. Then, when it is detected that the toner concentration reaches the upper limit value of the appropriate range,
The driving of the toner supply roller 21 is stopped. By such control, the toner concentration in the developing tank 16 is maintained within the proper range.

The toner replenished as described above is agitated with the developer in the developing tank 16 and controlled to a constant charge amount, supplied to the photoconductor 4 and used for development. on the other hand,
Since the carrier in the developer does not decrease and is repeatedly used, it is gradually deteriorated by stirring with the developing roller 17 and the stirring screw 18 and contact with the photoconductor 4. As the carrier deteriorates in this way, it becomes impossible to impart a predetermined charge amount to the toner, resulting in deterioration of image quality.

Therefore, the carrier is newly replenished in the developing tank 16 and replaced with the deteriorated carrier in the developing tank 16, so that the above-mentioned deterioration of the charging performance can be suppressed. For this reason, the controller 32 also controls the replenishment / discharge of replenishing the carrier developer from the carrier developer storage chamber and discharging the developer in the developing tank 16.

In this embodiment, as shown in FIG. 5, a magnet 36 for providing a magnetic field inside the recovery container 35 is provided near the outer periphery of the bottom outer wall of the developer recovery container 35. The magnet 36 is composed of a sheet-shaped magnet assembly in the illustrated example, but may be a normal permanent magnet. The magnet 36 disposed on the outer bottom portion of the recovery container 35 always applies a magnetic force to the discharged carrier developer, whereby the carrier developer charged from above into the container is flat and uniform. It is arranged to enter the recovery container 35.

That is, by installing the magnet 36 on the outer wall surface of the bottom of the recovery container 35, the carrier developer dropped below the developer overflow port 23a has a larger outer magnetic force than the central magnetic force. Is attracted to the outside by. Therefore, the discharged carrier developer is dispersed in the container in a flat and uniform state, so that the recovery space can be reduced, and the recovery amount can be increased even in the same space, which is effective in reducing the running cost. is there. In addition, if a sheet-shaped magnet assembly is used as the magnet 36, there are advantages that the cost is low, the place in the thickness direction is less restricted, and the shape can be easily changed.

FIG. 6 shows the discharged carrier developer collecting section in the second embodiment of the present invention. In this embodiment, a sheet-like magnet 37 that gives a magnetic field inside the container is provided on the outer surface of the side wall of the recovery container 35 used in the first embodiment.
In this case, due to the magnetic force of the magnet 37, the discharged carrier developer that has dropped below the developer overflow port adheres to the side wall of the collection container before it collects at the bottom of the container, preventing the discharged carrier developer from forming a mountain in the container. Then, it is uniformly dispersed in the container. Therefore, since the discharged developer is dispersed in the waste developer collecting container in a flat and uniform state, the collecting space can be reduced, and even in the same space,
Since the recovery amount is increased, the running cost can be reduced.

FIG. 7 shows the discharged carrier developer collecting section in the third embodiment of the present invention. In this embodiment, a sheet-shaped magnet 38 that gives a magnetic field to the interior of the copying machine is provided at the portion of the exterior body 40 of the copying machine facing the outside of the side wall of the recovery container 35 used in the first and second embodiments. in this case,
The discharged carrier developer dropped below the developer overflow port adheres to the outer wall of the container before being collected by the magnetic force at the bottom of the container, thereby preventing the discharged carrier developer from forming a hill in the container. Further, since the magnet 38 is provided on the exterior substrate 40 side, the shape of the collection container can be freely set,
In addition, running costs can be reduced.

FIG. 8 shows the discharged carrier developer collecting section in the fourth embodiment of the present invention. In this embodiment, an electromagnet 39 that gives a magnetic field to the container 35 is embedded in the exterior body of the copying machine facing the outside of the side wall of the recovery container 35 used in the first to third embodiments, and the inside of the container is discharged. The carrier developer is configured to be affected by the magnetic field. in this case,
The discharged carrier developer overflowing into the recovery container 35 is uniformly dispersed in the container under the influence of the magnetic field of the electromagnet 39.
Also in this embodiment, since the electromagnet 39 is provided on the exterior substrate 40 side, the shape of the recovery container can be freely set, and the running cost can be reduced.

In the present embodiment, the switch 41 controlled by the control device 32 is used to switch ON / OFF the energization of the electromagnet 39, and as shown in the time chart of FIG. Is controlled in synchronism with the operation timing of the developing device 8 and the timing of discharging the developer from the developing device 8 to energize the electromagnet 39 ON / OFF, thereby forming a magnetic field of the electromagnet 39, The discharged carrier developer in the recovery container 35, which is sucked depending on the presence or absence of the magnetic field, is flattened by its own weight, so that the recovery efficiency can be further improved.

In this case, as shown in the time chart of FIG. 9, the efficiency of collecting the discharged carrier developer can be improved by operating the electromagnet 39 only when the developing device is operating, that is, when the discharged carrier developer is discharged. Since the electromagnet 39 is not operated when the developer is not discharged,
The discharged carrier developer sucked by the electromagnet 39 is flattened by its own weight, and collection efficiency is further improved.

Further, in this embodiment, FIGS. 10A to 10C are used.
11 and the time chart of FIG. 11, the electromagnet 39 is always energized when the developing device 8 is not operating, that is, the electromagnet 39 is turned on / off in synchronization with the non-operating timing of the developing device 8. By controlling
By forming a magnetic field of the electromagnet 39, the attracted developer is flattened by its own weight depending on the presence or absence of the magnetic field, so that the recovery efficiency can be further improved. In this case, since the magnet is not energized when the developing device 8 is operating, the magnetic force of the electromagnet does not affect the magnetic brush on the developing roller 17 in the developing device 8 and a good image can be obtained.

12 and 13 (A) to 13 (C) show the discharged carrier developer collecting portion in the fifth embodiment of the present invention. In this embodiment, the opening / closing cover 4 at the front of the copying machine, which faces the outside of the side wall of the recovery container 35 used in the third embodiment.
2, a sheet-like magnet 43 that gives a magnetic field is arranged.

In this case, the distance between the magnet 43 and the discharged carrier developer in the container changes due to the opening / closing of the opening / closing cover 42 without using the electromagnet and its operation control device. Since the influence changes, when the influence is not applied, the discharged carrier developer attracted by the magnet 43 is flattened by its own weight, and the recovery efficiency is further improved. Further, as a result, the collection container 35
The shape of can be freely set, and running cost can be reduced.

FIG. 14 shows the discharged carrier developer collecting portion in the sixth embodiment of the present invention. In this embodiment, a U-shaped sheet magnet 44 is provided near the outer periphery of the outer surface of the bottom of the recovery container 35 used in the first embodiment. In this case, when the discharged carrier developer falls into the U-shaped hollow of the magnet 44 and becomes a mountain, the magnetic force acts outward so as to prevent the magnetic force from becoming a mountain. It can be efficiently flattened. As a result, the developer in the container can be easily dispersed, so that the shape of the recovery container can be freely set and the running cost can be reduced.

The time chart of FIG. 15 shows the relationship between the energization timing of the electromagnet 39 and the developing timing in the seventh embodiment of the present invention. Although not shown, in the present embodiment, the fourth opening and closing cover 42 at the front of the copying machine, which faces the outside of the side wall of the collection container 35, is the same as the fifth embodiment.
An electromagnet 39 that gives a magnetic field is provided as in the embodiment.

In this case, as shown in FIG. 15, after the completion of the developing operation, at a predetermined fixed timing,
ON / OFF energization is performed to create a magnetic field of the electromagnet 39,
The developer sucked by the presence or absence of the magnetic field is flattened by its own weight, the collection efficiency is further improved, the developing device 8 is not affected by the magnetic force of the electromagnet 39, and good image quality can be obtained by the minimum necessary current.

That is, when the developing device operates, the electromagnet 3
9 is not energized, the magnetic force of the electromagnet 39 does not affect the magnetic brush on the developing roller 17 in the developing device 8, and the amount of electricity can be reduced by energizing for a certain period of time. Therefore, as compared with the operation according to the time chart of FIG. 11, when the copying operation is not performed for a long time,
Since no more current than necessary is used for flattening the toner, it is possible to save power.

[0048]

As described above, according to the present invention, by installing the magnet on the outer wall of the bottom, the developer dropped below the developer overflow outlet has a large magnetic force (central magnetic force <outer magnetic force), Attracted to the outside. Therefore, since the discharged developer is dispersed in the recovery container in a flat and uniform state, the recovery space can be reduced, and the recovery amount can be increased even in the same space, so that the running cost can be reduced. it can.

[Brief description of drawings]

FIG. 1 is a plan view showing a developing device according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along the section line XX in FIG.

FIG. 3 is a control block diagram of a copying machine incorporating the apparatus of this embodiment.

FIG. 4 is a schematic configuration diagram thereof.

FIG. 5 is a cross-sectional view of an essential part showing a developer recovery section.

FIG. 6 is a cross-sectional view of essential parts showing a developer recovery section according to a second embodiment of the present invention.

FIG. 7 is a cross-sectional view of essential parts showing a developer recovery section according to a third embodiment of the present invention.

FIG. 8 is a cross-sectional view of essential parts showing a developer recovery unit according to a fourth embodiment of the present invention.

FIG. 9 is a chart showing the electromagnet energization timing when the developer is discharged.

FIG. 10 is an explanatory diagram of the process.

FIG. 11 is a chart showing an electromagnet energization timing when a developer is discharged by another method.

FIG. 12 is a cross-sectional view of essential parts showing a developer recovery section in a fifth embodiment of the present invention.

FIG. 13 is an explanatory diagram of the process.

FIG. 14 is a cross-sectional view of essential parts showing a developer recovery section according to a sixth embodiment of the present invention.

FIG. 15 is a chart showing the electromagnet energization timing when the developer is discharged in the seventh embodiment of the present invention.

FIG. 16 is a cross-sectional view of essential parts showing a state where a developer overflows in a conventional method.

[Explanation of symbols]

 4 Photoreceptor 8 Developing Device 16 Developing Tank 17 Developing Roller 18 Stirring Roller 23 Developer Overflow Portion 23a Developer Overflow Port 25 Developer Supply Unit 34 Toner Density Sensor 35 Recovery Container 36 Magnet 37 Magnet 38 Magnet 39 Electromagnet 40 Copier Exterior Substrate 41 switch 42 open / close cover 43 magnet 44 magnet

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Toyota 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Yoshiaki Ochi 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Incorporated (72) Inventor Masahiro Tsuji 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka

Claims (3)

[Claims] 1. A developing unit for visualizing an electrostatic latent image carried on the surface of a photoconductor using a magnetic developer, and a recovery container for accommodating used developer discharged from the developing unit. In the developing device, magnetic field applying means for applying a magnetic field to the inside of the recovery container is provided in the vicinity of the outer periphery of the recovery container. 2. A developing section for visualizing an electrostatic latent image carried on the surface of a photoconductor using a magnetic developer, and a recovery container for accommodating used developer discharged from the developing section. In the developing device, a magnet for applying a magnetic field to the inside of the recovery container is arranged along the outer bottom of the recovery container. 3. A developing tank for accommodating a developer composed of toner and carrier is provided rotatably with a stirring means for stirring the developer and a developing roller for supplying the developer to the photoconductor. Is provided with a toner concentration detecting means for detecting the toner concentration, and a developer replenishing portion for sequentially replenishing the developing tank with carrier developer containing toner or carrier based on a signal of the toner concentration detecting means. On the other hand, in the developing device, a developer overflow outlet for developer overflow is formed on the side wall portion of the developer tank, and the recovery device has a recovery container for storing the developer overflowed from the developer overflow outlet. A developing device, wherein a magnet for applying a magnetic field is disposed inside the recovery container along the outer bottom of the container.