Patent Publication Number: US-8989637-B2

Title: Developing device and image forming device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2012-154990 filed Jul. 10, 2012. 
     BACKGROUND 
     Technical Field 
     The present invention relates to a developing device and an image forming device. 
     SUMMARY 
     According to an aspect of the invention, there is provided a developing device including: a first developer holding member, disposed opposite to an image holding member that holds an electrostatic latent image and cyclically moves, which rotates in a reverse direction to the image holding member at an opposite location to the image holding member and holds and carries developer, containing toner and magnetic carrier, toward a first development area on which the electrostatic latent image on the image holding member is developed; a second developer holding member, disposed opposite to the image holding member and the first developer holding member at the side located further downstream of the image holding member in a direction of movement than the first developer holding member, which rotates in the same direction as the first developer holding member at an opposite location to the first developer holding member and holds and carries the developer toward a second development area on which the electrostatic latent image on the image holding member is developed; a developer supply mechanism that supplies the developer to a position located further downstream than the second development area in a direction of rotation of the second developer holding member and located further upstream than opposite locations of the two developer holding members, with respect to any one of the first and second developer holding members; a regulation member that regulates the developer supplied by the developer supply mechanism to an amount necessary to be provided for use in development at both the first and second developer holding members; a developer division unit that has dividing magnetic poles having polarities different from each other, respectively disposed at the opposite locations of the first and second developer holding members, and divides the developer, supplied from the developer supply mechanism due to a dividing magnetic field formed by the dividing magnetic poles and carried to the opposite locations of the two developer holding members, into two parts for the two developer holding members; and a developer carrying unit that has carrying magnetic poles, respectively, disposed between each of the dividing magnetic poles and each developing magnetic pole corresponding to each of the development areas in the first and second developer holding members, the carrying magnetic poles having a polarity different from both the poles, and holds and carries the developer after division toward each of the development areas in a state where the developer after division is separated, while increasing a magnetic flux density of a location adjacent to the developer division unit further than when the carrying magnetic poles are not present due to a magnetic flux density distribution of the carrying magnetic poles. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a schematic diagram illustrating an outline of an exemplary embodiment of a developing device to which the invention is applied; 
         FIG. 2A  is a diagram illustrating an action in a case where only dividing magnetic poles used in a developing device according to a comparative example are included, and  FIG. 2B  is a diagram illustrating an action in a case where dividing magnetic poles and carrying magnetic poles used in a developing device according to an exemplary embodiment are included; 
         FIG. 3  is a schematic diagram illustrating an outline of an image forming device according to Exemplary Embodiment 1; 
         FIG. 4  is a schematic diagram illustrating an outline of a developing device according to Exemplary Embodiment 1; 
         FIG. 5  is a diagram illustrating a magnetic pole arrangement according to Exemplary Embodiment 1; 
         FIG. 6  is a diagram illustrating a movement of developer in the developing device according to Exemplary Embodiment 1; 
         FIGS. 7A and 7B  are diagrams illustrating magnetic patterns in a case where the carrying magnetic poles are not included as a comparative example;  FIG. 7A  is a diagram illustrating a case where two developing rollers are separated from each other to such an extent that a magnetic action is not caused to act therebetween, and  FIG. 7B  is a diagram illustrating a case where two developing rollers are in close proximity to each other so as to cause a magnetic action to act therebetween; 
         FIGS. 8A and 8B  are diagrams illustrating magnetic patterns in a case where carrying magnetic poles are included as in Exemplary Embodiment 1;  FIG. 8A  is a diagram illustrating a case where two developing rollers are separated from each other to such an extent that a magnetic action is not caused to act therebetween, and  FIG. 8B  is a diagram illustrating a case where two developing rollers are in close proximity to each other so as to cause a magnetic action to act therebetween; 
         FIG. 9A  is a schematic diagram illustrating a flow of developer in a case where a regulation member is included between two developing rollers as a comparative example, and  FIG. 9B  is a diagram illustrating an example of a magnetic pattern thereof; 
         FIGS. 10A to 10C  are diagrams illustrating an action based on the magnetic pole arrangement of dividing magnetic poles;  FIG. 10A  is a diagram illustrating a case where a dividing magnetic pole of a first developing roller is biasedly disposed at the side located further upstream than a dividing magnetic pole of a second developing roller as in Exemplary Embodiment 1,  FIG. 10B  is a diagram illustrating a case where the dividing magnetic poles of the first developing roller and the second developing roller are disposed at positions opposite to each other, and  FIG. 10C  is a diagram illustrating a case where the dividing magnetic pole and a carrying magnetic pole of the first developing roller are biasedly disposed at the side located further downstream than the dividing magnetic pole of the second developing roller; 
         FIGS. 11A and 11B  are diagrams illustrating actions based on the size of magnetic pole widths (half-value widths) of the dividing magnetic pole and the carrying magnetic pole;  FIG. 11A  is a diagram illustrating a case where the carrying magnetic pole is larger than the dividing magnetic pole, and  FIG. 11B  is a diagram illustrating a case where the carrying magnetic pole is smaller than the dividing magnetic pole; 
         FIGS. 12A and 12B  are diagrams illustrating actions in a case where the position of the carrying magnetic pole is changed, and are diagrams illustrating cases where the carrying magnetic pole shown in  FIG. 12B  is disposed at a position closer to the dividing magnetic pole than that shown in  FIG. 12A ; 
         FIG. 13  is a diagram illustrating a movement of developer in a developing device of Exemplary Embodiment 2; 
         FIG. 14  is a schematic diagram illustrating an outline of a developing device of Exemplary Embodiment 3; 
         FIG. 15  is a diagram illustrating a movement of developer in the developing device of Exemplary Embodiment 3; 
         FIG. 16  is a diagram illustrating a movement of developer in a developing device of Exemplary Embodiment 4; 
         FIG. 17  is a schematic diagram illustrating an outline of a developing device of Exemplary Embodiment 5; 
         FIG. 18  is a diagram illustrating a movement of developer in a developing device of Exemplary Embodiment 5; 
         FIG. 19  is a diagram illustrating an example of magnetic patterns when seven-pole developing rollers of Example 1 are disposed opposite to each other; 
         FIG. 20  is a diagram illustrating an example of magnetic patterns when five-pole developing rollers are disposed opposite to each other as a comparative example; 
         FIG. 21  is a diagram illustrating an arrangement of evaluation models of example 2; 
         FIG. 22  is a graph showing a result of example 2, and is a graph illustrating a case where the half-value width of the carrying magnetic pole is 30°; and 
         FIG. 23  is a graph showing a result of example 2, and is a graph illustrating a case where the half-value width of the carrying magnetic pole is 20°. 
     
    
    
     DETAILED DESCRIPTION 
     Outline of Exemplary Embodiment 
     First, an outline of an exemplary embodiment of a developing device to which the invention is applied will be described. 
       FIG. 1  is a schematic diagram illustrating an outline of a developing device according to a model of an exemplary embodiment for embodying the invention. The developing device includes a first developer holding member  2 , disposed opposite to an image holding member  1  that holds an electrostatic latent image and cyclically moves, which rotates in a reverse direction to the image holding member  1  at an opposite location to the image holding member  1  and holds and carries developer G, containing toner and magnetic carrier, toward a development area Da on which the electrostatic latent image on the image holding member  1  is developed, a second developer holding member  3 , disposed opposite to the image holding member  1  and the first developer holding member  2  at the side located further downstream of the image holding member  1  in the direction of movement than the first developer holding member  2 , which rotates in the same direction as the first developer holding member  2  at an opposite location to the first developer holding member  2  and holds and carries the developer G toward a development area Db on which the electrostatic latent image on the image holding member  1  is developed, a developer supply mechanism  4  that supplies the developer G to a position located further downstream than the development area Db in the direction of rotation of the second developer holding member  3  and located further upstream than opposite locations of the two developer holding members  2  and  3 , with respect to any one of the first and second developer holding members  2  and  3 , a regulation member  5  that regulates the developer G supplied by the developer supply mechanism  4  to the amount necessary to be provided for use in development at both the first and second developer holding members  2  and  3 , a developer division unit  6  that has dividing magnetic poles  7  ( 7   a  and  7   b ) having polarities different from each other, respectively, disposed at the opposite locations of the first and second developer holding members  2  and  3 , and divides the developer G, supplied from the developer supply mechanism  4  due to a dividing magnetic field formed by the dividing magnetic poles  7  and carried to the opposite locations of the two developer holding members  2  and  3 , into two parts for the two developer holding members  2  and  3 , and a developer carrying unit  9  that has carrying magnetic poles  10  ( 10   a  and  10   b ), respectively, disposed between each of the dividing magnetic poles  7  and each of developing magnetic pole  8  ( 8   a  and  8   b ) corresponding to each of the development areas Da and Db in the first and second developer holding members  2  and  3 , the carrying magnetic poles  10  having a polarity different from both these poles, and holds and carries the developer G after division toward each of the development areas Da and Db in a state where the developer G is separated, while increasing a magnetic flux density of a location adjacent to the developer division unit  6  further than when the carrying magnetic poles  10  are not present due to a magnetic flux density distribution of the carrying magnetic poles  10 . 
     Here, the first and second developer holding members  2  and  3  just need to be able to hold and carry the developer (two-component developer) G containing toner and magnetic carrier on the peripheral surfaces thereof, and the peripheral surfaces of the two developer holding members  2  and  3  are subjected to grooving, roughening treatment or the like so that the developer G is carried. A typical example of such developer holding members  2  and  3  includes a configuration in which a non-magnetic cylindrical rotating member is included on the surfaces thereof, and a magnet member that has a permanent magnet fixedly disposed in the inside of the rotating member is included. 
     In addition, the developer supply mechanism  4  just needs to supply the developer G to any one of the first and second developer holding members  2  and  3 . In the present example, an example in which the developer G is supplied to the second developer holding member  3  side is shown, but the developer G may be supplied to the first developer holding member  2  side without being limited thereto. Further, since the regulation member  5  regulates the developer G so that the necessary amount of developer G is carried to the opposite locations of the two developer holding members  2  and  3 , the regulation member  5  may be provided opposite to the second developer holding member  3 , and may regulate the developer G before the developer G is supplied to the second developer holding member  3 . 
     The developer division unit  6  divides the developer G, carried to the opposite locations of the two developer holding members  2  and  3  in the second developer holding member  3 , into two parts for the first and second developer holding members  2  and  3 , and thus the developer G is divided due to a dividing magnetic field formed by the dividing magnetic poles  7  ( 7   a  and  7   b ) having polarities different from each other. Since members are not disposed on the opposite locations of the two developer holding members  2  and  3  by including such a developer division unit  6 , excessive stress is not also given to the developer G. In addition, when the developer G is divided, the developer G is divided by the dividing magnetic poles  7 . Therefore, even when the amount of developer G increases or decreases, the developer G is divided at a stable division ratio. Such dividing magnetic poles  7  ( 7   a  and  7   b ) may be disposed corresponding to nearest-neighbor locations of the two developer holding members  2  and  3 , and are allowed to be biased to each other within a range in which a dividing magnetic field acts. 
     In addition, the developer carrying unit  9  carries the developer G, divided into two parts for the two developer holding members  2  and  3  by the developer division unit  6 , toward each of the development areas Da and Db. The magnetic flux density of a location adjacent to the developer division unit  6  is increased due to the magnetic flux density distribution of such carrying magnetic poles  10 , the magnitude of the magnetic flux density of the carrying magnetic poles  10  is set to such a magnitude as to carry the developer G divided by the developer division unit  6  in a state where the developer G is separated, and the developer G after division is not delivered between the two developer holding members  2  and  3  due to a magnetic field caused by the carrying magnetic poles  10  after division. 
     Here, a flow of the developer G when the developer division unit  6  and the developer carrying unit  9  are included will be described. 
       FIG. 2A  is a diagram illustrating a flow of the developer G in an example in which each of the developer holding members  2  and  3  includes only the developer division unit  6  constituted by the dividing magnetic poles  7  ( 7   a  and  7   b ) and does not include the developer carrying unit  9 , as a comparative example, and  FIG. 2B  is a diagram illustrating a flow of the developer G in an example in which each of the developer holding members  2  and  3  includes the developer division unit  6  and the developer carrying unit  9 , as in the exemplary embodiment. 
     As shown in  FIG. 2A , in the example in which the first and second developer holding members  2  and  3  include only the developer division unit  6 , the flow of the developer G is thought to be as follows. The developer G supplied to the opposite locations of the two developer holding members  2  and  3  is divided into two parts for the two developer holding members  2  and  3  by the developer division unit  6  constituted by the dividing magnetic poles  7   a  and  7   b  having polarities different from each other. Here, both the developer holding members  2  and  3  do not have any magnetic poles between the dividing magnetic poles  7   a  and  7   b  and the developing magnetic poles  8   a  and  8   b  located at the development areas Da and Db. Therefore, in the developer G nipped by the dividing magnetic poles  7   a  and  7   b , a force received from the developer holding members  2  and  3  between the dividing magnetic poles  7   a  and  7   b  and the developing magnetic poles  8   a  and  8   b  considerably decreases. At this time, since the distances from the dividing magnetic poles  7   a  and  7   b  to the developing magnetic poles  8   a  and  8   b  are long, the divided developer G is not constrained by each of the developer holding members  2  and  3 , and thus the developer G peels off. For this reason, it is hard to stabilize the flow of the developer G after division, and the mutual contact of the developer G between each of the developer holding members  2  and  3  after division also tends to occur. Therefore, it is difficult to maintain the amount of developer G based on a stable division ratio in the developer G after division. Further, a variation in the layer thickness of the developer G reaching the developing magnetic poles  8   a  and  8   b  also increases, and thus there may be a concern of image non-uniformity, for example, being generated at the time of development. 
     On the other hand, as shown in  FIG. 2B , in the example in which the first and second developer holding members  2  and  3  include the developer division unit  6  and the developer carrying unit  9 , the flow of the developer G is thought to be as follows. In each of the developer holding members  2  and  3 , the developer division unit  6  constituted by the dividing magnetic poles  7   a  and  7   b  and the developer carrying unit  9  constituted by the carrying magnetic poles  10   a  and  10   b  are disposed close to each other, and the magnitude of the magnetic flux density is sufficiently secured between the dividing magnetic poles  7   a  and  7   b  and the carrying magnetic poles  10   a  and  10   b  in each of the developer holding members  2  and  3 . For this reason, the peeling off of the developer G after division from each of the developer holding members  2  and  3  is suppressed, and the developer G os sufficiently constrained by the developer holding members  2  and  3 . Thereby, the mutual contact of the developer G between each of the developer holding members  2  and  3  after division is also suppressed, and the developer G of which the amount of developer G having a stable division ratio in the developer G after division is maintained is carried toward each of the development areas Da and Db. In addition, in such developer G carried toward the development areas Da and Db, a variation in the layer thickness of the developer G is suppressed to an extent that the peeling off thereof from each of the developer holding members  2  and  3  is suppressed, and the occurrence of image non-uniformity is also suppressed at the time of development. 
     Further, in  FIG. 1 , from the viewpoint of dividing the developer G through the developer division unit  6  at a division ratio which is set in advance, the developer division unit  6  is preferably configured such that the central position of a magnetic pole width along the circumferential direction of the dividing magnetic pole  7   a  of the first developer holding member  2 , out of the dividing magnetic poles  7   a  and  7   b , located on a different side from the second developer holding member  3  to which the developer G is supplied by the developer supply mechanism  4  is set to be biased toward the upstream side of the first developer holding member  2  in the direction of rotation, with respect to the central position of a magnetic pole width along the circumferential direction of the dividing magnetic pole  7   b  of the second developer holding member  3  to which the developer G is supplied by the developer supply mechanism  4 . In this manner, one dividing magnetic pole  7   a  is biased further toward the upstream side than the other, and thus an action of suctioning the developer G to the first developer holding member  2  side is caused to be exerted against a developer carrying force of the developer G carried onto the second developer holding member  3  toward the opposite location. Further, thereafter, an action of returning a portion of the developer G suctioned a great deal is caused to be exerted, and thus the developer G is divided at a division ratio which is set in advance. At this time, peak values of a normal component of magnetic flux density in the two dividing magnetic poles  7   a  and  7   b  are made approximately equal to each other, and thus the division ratio is easily divided equally. In addition, when the peak values of a normal component of magnetic flux density in the two dividing magnetic poles  7   a  and  7   b  are changed, the division ratio changes depending on the peak values. Meanwhile, a detailed description thereof will be made later. 
     In addition, from the viewpoint of further stabilizing the flow of the developer G divided by the developer division unit  6 , when a half-value width of a normal component of magnetic flux density caused by the dividing magnetic pole  7  of each of the developer holding members  2  and  3  is set to θ1, and a half-value width of a normal component of magnetic flux density caused by the carrying magnetic pole  10  is set to θ2, both the dividing magnetic pole  7  and the carrying magnetic pole  10  in each of the developer holding members  2  and  3  are preferably set to satisfy a relationship of θ1&lt;θ2. In this manner, the half-value width of the carrying magnetic pole  10  is made to be larger than the half-value width of the dividing magnetic pole  7 , and thus the magnetic flux density acting on the developer G immediately after division increases, which leads to a further suppression of the peeling off of the developer G immediately after division from the developer holding members  2  and  3 . Meanwhile, a detailed description thereof will be made later. 
     Further, from the viewpoint of further suppressing the peeling off of the developer G from the developer holding members  2  and  3  at the time of carrying the developer G in the developer carrying unit  9 , the developer carrying unit  9  is preferably configured such that the central position of a magnetic pole width along the circumferential direction of the carrying magnetic pole  10   a  on the first developer holding member  2  side, out of the carrying magnetic poles  10 , located on a different side from the second developer holding member  3  to which the developer G is supplied by the developer supply mechanism  4  is set to be biased toward the upstream side of the first developer holding member  2  in the direction of rotation, with respect to the central position of a magnetic pole width along the circumferential direction of the carrying magnetic pole  10   b  of the second developer holding member  3  to which the developer G is supplied by the developer supply mechanism  4 . When the carrying magnetic poles  10   a  and  10   b  are thus biasedly disposed, the developer G divided to the first developer holding member  2  to which the developer G is not supplied can be further prevented from peeled off from the first developer holding member  2 , which leads to a further stabilization of the carrying of the developer G. In such a biased arrangement, it is suitable that both the dividing magnetic pole  7   a  and the carrying magnetic pole  10   a  of the first developer holding member  2  to which the developer G is not supplied be biasedly disposed at the upstream side. 
     In addition, from the viewpoint of improving the carrying property of the developer G while simplifying the configurations of the developer holding members  2  and  3 , preferably, the second developer holding member  3  to which the developer G is supplied by the developer supply mechanism  4  includes at least the developing magnetic pole  8   b , the dividing magnetic pole  7   b  and the carrying magnetic pole  10   b , and includes seven magnetic poles in the inside thereof along the direction of rotation of the second developer holding member  3 . Seven magnetic poles are included, so that it is possible to cause the second developer holding member  3  to have functions of the suction of the developer G to the regulation, division, carrying, development, carrying, and peeling thereof, and operations from the attachment of the developer G to the peeling off thereof are effectively performed in the second developer holding member  3 . 
     In order to apply such a developing device to an image forming device, the image holding member  1  that holds an electrostatic latent image and cyclically moves and the above-mentioned developing device as a developing device which is provided opposite to the image holding member  1  and develops the electrostatic latent image on the image holding member  1  with the developer G may be used. Such an image holding member  1  may be not only drum-shaped, but also belt-shaped. 
     In addition, the image forming device is not limited to an example in which the first and second developer holding members  2  and  3  are included, but an additional developer holding member may be applied to one image holding member  1  in addition to the first and second developer holding members  2  and  3 . Such an example includes the following example. That is, one or plural additional developer holding members, provided separately from the first and second developer holding members  2  and  3 , which are disposed opposite to the image holding member  1  and hold and carry the developer G toward a development area opposite to the image holding member  1 , and a delivery unit that delivers the developer G, held and carried on the first and second developer holding members  2  and  3 , to the additional developer holding members may be included. 
     Here, the additional developer holding members may be disposed on one side of the first and second developer holding members  2  and  3 , or may be disposed on both sides. In addition, an additional developer holding member is allowed to be included at the side located further upstream or downstream than the additional developer holding member with the delivery unit interposed therebetween. 
     The developer carrying unit  9  can include plural carrying magnetic poles  10  in each of the developer holding members  2  and  3 . In this case, the developing device may be configured as follows. That is, the developing device may include the first developer holding member  2 , disposed opposite to the image holding member  1  that holds an electrostatic latent image and cyclically moves, which rotates in a reverse direction to the image holding member  1  at an opposite location to the image holding member  1  and holds and carries developer G, containing toner and magnetic carrier, toward a development area Da on which the electrostatic latent image on the image holding member  1  is developed, the second developer holding member  3 , disposed opposite to the image holding member  1  and the first developer holding member  2  at the side located further downstream of the image holding member  1  in the direction of movement than the first developer holding member  2 , which rotates in the same direction as the first developer holding member  2  at an opposite location to the first developer holding member  2  and holds and carries the developer G toward a development area Db on which the electrostatic latent image on the image holding member  1  is developed, the developer supply mechanism  4  that supplies the developer G to a position located further downstream than the development area Db in the direction of rotation of the second developer holding member  3  and located further upstream than opposite locations of the two developer holding members  2  and  3 , with respect to any one of the first and second developer holding members  2  and  3 , the regulation member  5  that regulates the developer G supplied by the developer supply mechanism  4  to the amount necessary to be provided for use in development at both the first and second developer holding members  2  and  3 , the developer division unit  6  that has dividing magnetic poles  7  having polarities different from each other, respectively, disposed at the opposite locations of the first and second developer holding members  2  and  3 , and divides the developer G, supplied from the developer supply mechanism  4  due to a dividing magnetic field formed by the dividing magnetic poles  7  and carried to the opposite locations of the two developer holding members  2  and  3 , into two parts for the two developer holding members  2  and  3 , and the developer carrying unit  9  that has one or more carrying magnetic poles  10  disposed between each of the dividing magnetic poles  7  and each developing magnetic pole  8  corresponding to each of the development areas Da and Db in the first and second developer holding members  2  and  3  so that magnetic poles adjacent to each other including the dividing magnetic poles  7  and developing magnetic poles  8  have different polarities, and holds and carries the developer G after division toward each of the development areas Da and Db in a state where the developer is separated, while increasing a magnetic flux density of a location adjacent to the developer division unit  6  further than when the carrying magnetic poles  10  are not present due to a magnetic flux density distribution of the carrying magnetic poles  10 . In such an example, the number of carrying magnetic poles  10  is not limited, but plural carrying magnetic poles  10  may be included in both of each of the developer holding members  2  and  3 , and one carrying magnetic pole  10  may be included in one side and plural carrying magnetic poles  10  may be included in the other side. 
     Next, the invention will be described in more detail on the basis of exemplary embodiments shown in the drawings. 
     Exemplary Embodiment 1 
       FIG. 3  is a schematic diagram illustrating an outline of an image forming device of Exemplary Embodiment 1 using the developing device to which the invention is applied. In the same drawing, the image forming device of the exemplary embodiment is configured such that, for example, an electrophotographic system is adopted, and imaging devices  20  ( 20   a  to  20   d ) that performs imaging by four-color developer (two-component developer) containing toner and magnetic carrier are disposed side by side on the approximately linear portion of an intermediate transfer belt  30  that cyclically rotates. 
     &lt;Entire Configuration of Image Forming Device&gt; 
     Since each of the imaging devices  20  (specifically,  20   a  to  20   d ) has substantially the same configuration, one imaging device  20   a  will be described herein as the typical imaging device  20 . The imaging device  20  includes a photoreceptor  21  as an image holding member that holds an electrostatic latent image and rotates, a developing device  40 , provided opposite to the photoreceptor  21 , which develops the electrostatic latent image on the photoreceptor  21  with developer, and the like. Further, the periphery of the photoreceptor  21  is provided with a charger  22  for charging a photosensitive layer of the photoreceptor  21  to a potential which is set in advance, an exposure unit  23  that performs exposure so that a latent image based on an image signal is formed on the photoreceptor  21  charged by the charger  22 , the above-mentioned developing device  40  that develops the latent image formed by the exposure using the exposure unit  23  with developer and visualizes the latent image, a primary transfer roller  24  that transfers a toner image visualized by the developing device  40  onto the intermediate transfer belt  30 , a cleaning unit  25  that cleans off residues on the photoreceptor  21  after the toner image is transferred, and the like. 
     Here, an example of a corona charger is shown as the charger  22 , but, for example, a contact-type charging system is allowed to be adopted without being limited thereto. In addition, an example of an LED array type is shown as the exposure unit  23 , but, for example, a laser scanning type may be adopted. Further, an example of contact with the intermediate transfer belt  30  is shown as the primary transfer roller  24 , but a system in which the primary transfer roller is separated from the intermediate transfer belt  30 , for example, using a corona charger may be adopted. 
     The intermediate transfer belt  30  is hung over plural tension rollers  31  to  33 , and cyclically rotates using, for example, the tension roller  31  as a driving roller. Further, a secondary transfer roller  34  is disposed at a position opposite to the tension roller  33  with the intermediate transfer belt  30  interposed therebetween. Using the tension roller  33  as a back-up roller, a secondary transfer electric field is caused to act between the secondary transfer roller  34  and the back-up roller  33 , and thus a toner image on the intermediate transfer belt  30  is transferred onto a recording material P. Reference numeral  35  in the drawing denotes a belt cleaning unit that cleans off residual toner on the intermediate transfer belt  30 . Meanwhile, in the present example, an example in which the intermediate transfer belt  30  is used is shown, but, for example, a drum-shaped intermediate transfer member may be used instead of the intermediate transfer belt  30 . Further, using a recording material transport belt that holds and carries a recording material instead of the intermediate transfer belt  30 , toner images created by the imaging devices  20  may be sequentially transferred onto the recording material held on the recording material transport belt. 
     In addition, in the exemplary embodiment, the recording material P is supplied to a secondary transfer location, a transporting path of the recording material P before the recording material P is discharged from the secondary transfer location is provided, and the transporting path is provided with the following members. Registration rollers  36  that position the recording material P directed toward the secondary transfer location and transport the positioned recording material P toward the secondary transfer location at a preset timing are provided at positions adjacent to each other at the upstream side of the secondary transfer location in the transporting direction of the recording material P. In addition, a transport belt  37  that transports the recording material P to which the toner image is transferred at the secondary transfer location, fixing rollers  38  that fix a non-fixed toner image on the recording material P at the downstream side of the transport belt  37 , discharge rollers  39  that discharge the recording material P, to which the non-fixed toner image is fixed by the fixing rollers  38  at the downstream side of the fixing rollers  38 , to the outside of the image forming device, and the like are disposed at the side located further downstream than the secondary transfer location. 
     &lt;Configuration of Developing Device&gt; 
     The developing device  40  of the exemplary embodiment is formed as shown in  FIG. 4 . The developing device  40  is provided with two developer holding members disposed opposite to the photoreceptor  21 , corresponding to an opening of a developing container  41 . These developer holding members are constituted by a first developing roller  42 A as a first developer holding member and a second developing roller  42 B as a second developer holding member. The first developing roller  42 A rotates in a reverse direction to the photoreceptor  21  at the opposite location to the photoreceptor  21 , and holds and carries developer containing toner and magnetic carrier toward a development area DA. On the other hand, the second developing roller  42 B is disposed at the side located further downstream than the first developing roller  42 A in the direction of rotation of the photoreceptor  21 , rotates in the same direction as the photoreceptor  21  at the opposite location to the photoreceptor  21 , and holds and carries the developer toward a development area DB. 
     The first developing roller  42 A includes a developing sleeve  43 A (non-magnetic cylindrical rotating member) that holds and carries the developer on the peripheral surface and a magnet member  44 A which is fixedly provided within the developing sleeve  43 A and in which a magnet is disposed in the magnetic pole arrangement set in advance. In addition, similarly to the first developing roller  42 A, the second developing roller  42 B also includes a developing sleeve  43 B that holds and carries the developer on the peripheral surface and a magnet member  44 B which is fixedly provided within the developing sleeve  43 B and in which a magnet is disposed in the magnetic pole arrangement set in advance. On the peripheral surface of each of the developing sleeves  43 A and  43 B, V-shaped grooves, for example, extending along the width direction intersecting the direction of rotation thereof are formed at intervals set in advance along the direction of rotation. 
     In the magnetic pole arrangement in the magnet members  44 A and  44 B, each magnetic pole is disposed so that the developer is sufficiently carried, and in the present example, both the magnet members  44 A and  44 B have seven magnetic poles disposed in the insides thereof along the direction of rotation. In the magnet member  44 A of the first developing roller  42 A, an N1 pole as a developing magnetic pole  62  corresponding to the development area DA is disposed, and an S1 pole, an N2 pole, an S2 pole, an S3 pole, an N3 pole, and an S4 pole are disposed in order along the direction of rotation of the first developing roller  42 A. Here, the S1 pole and the N2 pole are magnetic poles for carrying the developer. The S2 pole is a magnetic pole for peeling off the developer from the first developing roller  42 A, and peels off the developer from the first developing roller  42 A due to a repulsion magnetic field between the S2 pole and the S3 pole, having the same polarity, which are adjacent to each other at the downstream side. In addition, the N3 pole is a dividing magnetic pole  61  constituting the developer division unit, and the S4 pole is a carrying magnetic pole  63  constituting the developer carrying unit. 
     On the other hand, in the magnet member  44 B of the second developing roller  42 B, an S1 pole as a developing magnetic pole  62  is disposed at a position corresponding to the development area DB, and an N1 pole, an S2 pole, an S3 pole, an N2 pole, an S4 pole, and an N3 pole are disposed in order along the direction of rotation of the second developing roller  42 B. Here, the N1 pole is a magnetic pole for carrying the developer. The S2 pole is a magnetic pole for peeling off the developer from the second developing roller  42 B, and peels off the developer from the second developing roller  42 B due to a repulsion magnetic field between the S2 pole and the S3 pole, having the same polarity, which are adjacent to each other at the downstream side. The S3 pole is a magnetic pole for suctioning the developer to the second developing roller  42 B, and the developer is supplied to the second developing roller  42 B due to a suction action of the S3 pole. In addition, the N2 pole is a regulating magnetic pole disposed for a regulation member  45  (described later) that regulates the layer thickness of the developer supplied to the second developing roller  42 B. Further, the S4 pole is the dividing magnetic pole  61  constituting the developer division unit, and the N3 pole is the carrying magnetic pole  63  constituting the developer carrying unit. Meanwhile, the magnetic pole arrangement in the first developing roller  42 A and the second developing roller  42 B is not limited to the above example, but may be appropriately selected without interfering with the flow of the developer. 
     The dividing magnetic poles  61  and the carrying magnetic poles  63  of the exemplary embodiment are disposed as shown in  FIG. 5 . That is, in the first developing roller  42 A, the angle between a line segment that links a central axis OA and the center of the dividing magnetic pole  61  in the circumferential direction and a line segment that links the central axis OA and the center of the carrying magnetic pole  63  in the circumferential direction is α+β. On the other hand, in the second developing roller  42 B, the angle between a line segment that links a central axis OB and the center of the dividing magnetic pole  61  in the circumferential direction and a line segment that links the central axis OB and the center of the carrying magnetic pole  63  in the circumferential direction is β. That is, the dividing magnetic pole  61  of the first developing roller  42 A is disposed to be biased by the angle α at the side located further upstream in the direction of rotation of the first developing roller  42 A than a line segment that links the central axis OA of the first developing roller  42 A and the central axis OB of the second developing roller  42 B. 
     Here, the first developing roller  42 A and the second developing roller  42 B of the exemplary embodiment are configured so that the line segment that links the mutual central axes OA and OB is directed toward the vertical direction, in order to make it easier to understand, but specifically as shown in  FIG. 4 , these rollers are disposed with an inclination of 7 degrees or so (first developing roller  42 A is inclined toward the photoreceptor  21  side). In addition, sign g1 in the drawing means a gap between the first developing roller  42 A and the second developing roller  42 B. Meanwhile, in  FIG. 5 , the dividing magnetic pole  61  (S4) is located on the line that links the central axes OA and OB, but is obviously not limited thereto. 
     Further, power supplies  56 A and  56 B, for example, for supplying a voltage obtained by superimposing an alternating electric field on a direct electric field are connected to the first developing roller  42 A and the second developing roller  42 B, and a development electric field is caused to act between, for example, the grounded photoreceptor  21  and each of the developing rollers  42 A and  42 B. 
     Two resin blocks  47   a  and  47   b  supported by the developing container  41  are disposed behind the first developing roller  42 A and the second developing roller  42 B within the developing container  41 . The regulation member  45  is installed on these resin blocks  47   a  and  47   b , and is configured to regulate the layer thickness of the developer on the second developing roller  42 B between the regulation member  45  and the N2 pole as a regulating magnetic pole of the second developing roller  42 B. The regulation member  45  of the exemplary embodiment is constituted by a regulating piece  45   a  which is disposed on the side close to the N2 pole of the second developing roller  42 B and is made of a magnetic material and a regulating plate  45   b  which is disposed next to the regulating piece  45   a  at the side located further downstream in the direction of rotation of the second developing roller  42 B than the regulating piece  45   a  and is made of a non-magnetic material having a larger thickness than that of the regulating piece  45   a . In addition, a guide member  46  that guides the developer peeled off from the first developing roller  42 A downward is obliquely provided above the resin block  47   a.    
     Further, a developer stirring mechanism, which stirs and carries developer, for supplying the stirred developer to the second developing roller  42 B is provided behind the second developing roller  42 B within the developing container  41 . The developer stirring mechanism includes two developer carrying paths  51  and  52  extending substantially parallel to each other using a partition wall  41   a  (constituting a portion of the developing container  41 ) extending along the axial directions of the first and second developing rollers  42 A and  42 B as a boundary, and the developer carrying paths  51  and  52  are respectively provided with stirring carrying members  53  and  54  that stir and carry the developer by rotating a spiral blade. In addition, passages, not shown, which connect the two developer carrying paths  51  and  52  are formed at both ends of the partition wall  41   a  in the axial directions of the stirring carrying members  53  and  54 , and the developer can circulate between the two developer carrying paths  51  and  52  through these passages. In the exemplary embodiment, the stirring carrying member  53  located on the side close to the second developing roller  42 B, out of the two stirring carrying members  53  and  54 , is a member that mainly supplies the developer to the second developing roller  42 B, and the other stirring carrying member  54  is a member that mainly stirs the developer and charges the developer to a desired amount of electric charge. 
     Further, a hole is formed in a portion of the developing container  41  at an obliquely downward location of the developer carrying path  52  located on the side far from the second developing roller  42 B, and a permeability-type density sensor  55  that detects toner density in the developer by detecting a change in permeability is installed corresponding to this hole. Meanwhile, it goes without saying that the developer carrying path  52  is replenished with toner or is replenished with developer obtained by mixing toner and magnetic carrier, for example, using a replenishing mechanism which is not shown. 
     In the exemplary embodiment, particularly, the developing device  40  includes a developer division unit that divides developer on the second developing roller  42 B regulated by the regulation member  45  into two parts for the developing rollers  42 A and  42 B at the opposite locations of the two developing rollers  42 A and  42 B and a developer carrying unit that carries the developer divided by the developer division unit toward each of the development areas DA and DB. Specifically, the first developing roller  42 A and the second developing roller  42 B are respectively provided with the dividing magnetic poles  61  (equivalent to the N3 pole of the first developing roller  42 A and the S4 pole of the second developing roller  42 B) having polarities different from each other, and the carrying magnetic poles  63  (equivalent to the S4 pole of the first developing roller  42 A and the N3 pole of the second developing roller  42 B) which are provided on the side located further downstream in the direction of rotation of the developing rollers  42 A and  42 B than the dividing magnetic poles  61  and have polarities different from those of the dividing magnetic poles  61 . 
     In addition, the magnetic flux densities of the dividing magnetic poles  61  and the carrying magnetic poles  63  are as follows. Regarding the peak values of normal components of the magnetic flux densities of the dividing magnetic poles  61  (equivalent to the N3 pole of the first developing roller  42 A and the S4 pole of the second developing roller  42 B) and the carrying magnetic poles  63  (equivalent to the S4 pole of the first developing roller  42 A and the N3 pole of the second developing roller  42 B), the dividing magnetic poles  61  are smaller than the carrying magnetic poles  63  in a single developing roller, and the carrying magnetic poles  63  are smaller than the dividing magnetic poles  61  when two developing rollers are disposed opposite to each other. Further, the peak value of a normal component of the magnetic flux density of the magnetic poles has such a size that the developer is not delivered between the S4 pole of the first developing roller  42 A and the N3 pole of the second developing roller  42 B as the carrying magnetic poles  63 . Meanwhile, the peak values of normal components of the magnetic flux densities of the dividing magnetic poles  61  and the carrying magnetic poles  63  in the first and second developing rollers  42 A and  42 B are substantially the same as each other. 
     &lt;Operation of Image Forming Device&gt; 
     As shown in  FIG. 3 , in the image forming device of the exemplary embodiment, a toner image formed on the photoreceptor  21  of each of four imaging devices  20  is sequentially transferred onto the intermediate transfer belt  30  at the primary transfer location which is an opposite location to the primary transfer roller  24 , and a multiplexed toner image is formed on the intermediate transfer belt  30 . The multiplexed toner image which is multiplexed on the intermediate transfer belt  30  is secondarily transferred onto the recording material P supplied from a recording material supply unit, not shown, at the secondary transfer location which is an opposite location to the secondary transfer roller  34 . The recording material P onto which the toner image is transferred is transported to the fixing rollers  38  by way of the transport belt  37 , and is fixed by the fixing rollers  38 , and then is discharged by the discharge rollers  39  to, for example, a recording material receiving unit outside the device. 
     &lt;Operation of Developing Device&gt; 
       FIG. 6  is a diagram illustrating a movement of the developer G centering on the first developing roller  42 A and the second developing roller  42 B, and operations in the developing device  40  will be described with reference to the drawing. 
     The developer G supplied onto the second developing roller  42 B by the suction action of the S3 pole of the second developing roller  42 B is sufficiently nipped between the N2 pole as a regulating magnetic pole and the regulation member  45 , and the layer thickness of the developer G is regulated due to a gap between the nearest-neighbor locations of the regulation member  45  and the second developing roller  42 B. A portion of the developer G on the second developing roller  42 B regulated by the regulation member  45  moves from the second developing roller  42 B side to the first developing roller  42 A side by the suction action caused by a normal component of each magnetic flux density between two magnetic poles, that is, the pole as the dividing magnetic pole  61  on the second developing roller  42 B side and the N3 pole as the dividing magnetic pole  61  on the first developing roller  42 A side, and the residual thereof moves to the second developing roller  42 B, and thus is divided into two parts. For this reason, the divided developer G is held on each of the developing rollers  42 A and  42 B. Hereinafter, in order to make it easier to understand, the developer on the first developing roller  42 A after division is expressed as G1, and the developer on the second developing roller  42 B after division is expressed as G2. 
     In the exemplary embodiment, since the S4 pole and the N3 pole as the carrying magnetic poles  63  are provided between the N3 pole of the first developing roller  42 A and the S4 pole of the second developing roller  42 B as the dividing magnetic poles  61 , and the N1 pole of the first developing roller  42 A and the S1 pole of the second developing roller  42 B as the developing magnetic poles  62 , as shown in  FIGS. 2A and 25 , the peeling off of the developer G1 and the developer G2 after division from the developing rollers  42 A and  42 B is suppressed, and the developer is carried toward each of the development areas DA and DB as it is. For this reason, the developer G1 and the developer G2 after division maintain the amount of developer corresponding to the division ratio of the developer division unit, and are carried toward each of the development areas DA and DB as developer layers having a small variation in layer thickness. 
     —With Respect to Developer Division Action of Developing Device According to Comparative Example— 
     First, a description will be made of magnetic patterns in an example in which the carrying magnetic poles  63  are not included as a comparative example, that is, the dividing magnetic poles  61  and the developing magnetic poles  62  are disposed next to each other. Meanwhile, the normal components of the magnetic flux densities of the dividing magnetic poles  61 , the developing magnetic poles  62  and the carrying magnetic poles  63  in two developing rollers  42 A and  42 B are set to be the same as each other. 
       FIG. 7A  is a diagram illustrating an example of a magnetic pattern in a state where the carrying magnetic pole  63  is not included, and two developing rollers  42 A′ and  42 B′ are separated by a distance (equivalent to g0 in the drawing) beyond a mutual magnetic action. Each of the developing rollers  42 A′ and  42 B′ shows the same magnetic pattern. Due to a normal component Ra of the magnetic flux density caused by the dividing magnetic pole  61  and a normal component Rb of the magnetic flux density caused by the developing magnetic pole  62 , the peak value of a tangential component Ta of the magnetic flux density between both appears in substantially the center of two magnetic poles (dividing magnetic pole  61  and developing magnetic pole  62 ). 
     In order to dispose two developing rollers  42 A′ and  42 B′ to be opposite to each other and to divide the developer only using the heteropolar dividing magnetic poles  61 , it is necessary to dispose two developing rollers  42 A′ and  42 B′ at positions close to each other and to exert a sufficient magnetic action. When the developing rollers  42 A′ and  42 B′ are brought close to each other (equivalent to g1 in the drawing: g1&lt;&lt;g0) to such an extent that the developer is divided due to the magnetic action of the dividing magnetic poles  61 , a change in the magnetic pattern occurs as shown in  FIG. 7B . That is, the heteropolar dividing magnetic poles  61  are disposed close to each other, so that the peak value of a normal component Ra′ of the magnetic flux density caused by the dividing magnetic poles  61  becomes larger than that of the normal component Ra shown in  FIG. 7A . Thereby, a tangential component Ta′ of the magnetic flux density changes from the tangential component Ta shown in  FIG. 7A , and the peak value thereof moves to the developing magnetic pole  62  side. For this reason, in the tangential component Ta′, particularly, the size of the portion (portion indicated by Q in the drawing), shown in  FIG. 7B , in which the normal components (Ra and Ra′) of the dividing magnetic poles  61  start to decrease becomes smaller than that in  FIG. 7A . Meanwhile, in  FIG. 7B , the portion of Q on the developing roller  42 B′ side is omitted. 
     As stated above, when the tangential component of the magnetic flux density is small in a region in which the magnetic flux density in the normal direction is small between the dividing magnetic poles  61  and the developing magnetic poles  62 , as shown in  FIGS. 2A and 2B , the developer divided by the dividing magnetic poles  61  tends to be peeled off from the developing rollers  42 A′ and  42 B′ due to a decreasing constraining force acting on the developing rollers  42 A′ and  42 B′. As stated above, when the developer is divided only due to the magnetic action of the dividing magnetic poles  61  in the division location (equivalent to the developer division unit), the two developing rollers  42 A′ and  42 B′ have to be disposed in close proximity to each other. Therefore, a carrying force acting on the developer after division decreases, and the carrying of the developer becomes unstable. 
     —With respect to Division Action of Developer of Developing Device According to Exemplary Embodiment— 
     On the other hand, as in the exemplary embodiment, it is advantageous that the carrying magnetic pole  63  that increases a carrying force of the developer be included between the dividing magnetic pole  61  and the developing magnetic pole  62  (having a normal component R3 of magnetic flux density).  FIGS. 8A and 8B  are diagrams illustrating magnetic patterns when the carrying magnetic pole  63  is included between the dividing magnetic pole  61  and the developing magnetic pole  62  as in the exemplary embodiment;  FIG. 8A  is a diagram illustrating a state where two developing rollers  42 A and  42 B are separated by a distance (equivalent to g0 in the drawing) beyond a mutual magnetic action, and  FIG. 8B  is a diagram illustrating a state where these rollers are disposed in close proximity to each other (equivalent to g1 in the drawing: g1&lt;&lt;g0). 
     Similarly to  FIGS. 7A and 7B , in  FIG. 8A , due to the normal component R1 of the magnetic flux density caused by the dividing magnetic pole  61  and the normal component R2 of the magnetic flux density caused by the carrying magnetic pole  63 , the peak value of a tangential component T1 of the magnetic flux density between both appears in substantially the center of two magnetic poles (dividing magnetic pole  61  and the carrying magnetic pole  63 ). However, when such developing rollers  42 A and  42 B are disposed in close proximity to each other, as shown in  FIG. 8B , the peak value of the normal component R1′ of the magnetic flux density of the dividing magnetic pole  61  considerably increases as compared to the case of  FIG. 8A . Therefore, a tangential component T1′ of the magnetic flux density between the dividing magnetic pole  61  and the carrying magnetic pole  63  also changes as compared to the case of  FIG. 8A . In this case, the peak position of the tangential component T1′ changes slightly toward the carrying magnetic pole  63 . However, since the carrying magnetic pole  63  is located close to the dividing magnetic pole  61 , this state is different from that of  FIG. 7B  in which the carrying magnetic pole  63  is not included. In addition, the peak value of the tangential component T1′ slightly decreases as compared to  FIG. 8A , but the size of the portion (portion indicated by Q in the drawing) in which the normal component R1 of the dividing magnetic pole  61  starts to decrease is secured to some extent. This shows that a tangential component having a larger size than that of the tangential component Ta′ in the portion of Q shown in  FIG. 7B  is obtained. Meanwhile, in  FIG. 8B , the portion of Q on the developing roller  42 B side will be omitted. 
     Thereby, a sufficient carrying force is given to the developer immediately after division by providing the carrying magnetic poles  63 , and the peeling off of the developer after division from each of the developing rollers  42 A and  42 B is suppressed, thereby allowing the developer having stable layer thickness to be carried toward each of the development areas DA and DB. 
     Incidentally, as in a comparative example shown in  FIGS. 9A and 9B , a system is known in which two developing rollers  201  and  202  are disposed opposite to each other, and the developer G is divided into two parts for the two developing rollers  201  and  202  by providing a regulation member  203  in a gap g″ between both. Here,  FIG. 9A  is a schematic diagram illustrating a flow of the developer G, and  FIG. 9B  is a diagram illustrating a magnetic pattern. 
     This is configured such that the developer G is supplied extending over two developing rollers  201  and  202  at the upstream side of the regulation member  203 , and the layer thickness of the developer G is determined based on the regulation member  203  and a gap g′ between the developing rollers  201  and  202 . The developing rollers  201  and  202  are respectively provided with heteropolar magnetic poles  204  and  205  at positions opposite to the regulation member  203 , and the developing roller  202  is provided with a magnetic pole  206  at the downstream side of the magnetic pole  205 . In addition, gaps in such a configuration include a gap g′ between the developing rollers  201  and  202  and the regulation member  203 , and a gap g″ between the developing rollers  201  and  202 , and these gaps have a relationship of g′&lt;g1&lt;&lt;g″ in the exemplary embodiment (see  FIG. 5 ). 
     In the comparative example, normal components Rc and Rd of magnetic flux densities of two magnetic poles  204  and  205  disposed opposite to the regulation member  203  do not have such a size that the magnetic poles  204  and  205  exert an interaction, and merely cause a magnetic action at the gap g′ between the regulation member  203  and the magnetic poles. For this reason, the peak value of a tangential component Td of a magnetic flux density between the magnetic pole  205  and the magnetic pole  206  (normal component Re of a magnetic flux density) in the developing roller  202  is small. In such an example, since the retention of the developer G is caused to be generated at the upstream side of the regulation member  203 , an extra load acts on the developer G. In addition, when the magnetic forces of the two magnetic poles  204  and  205  opposite to the regulation member  203  are attempted to be strengthened, the retention action of the developer G at the upstream side of the regulation member  203  is strengthened instead, which leads to an undesirable result. 
     —With Respect to Action When Dividing Magnetic Poles Are Caused to Be Biased— 
       FIGS. 10A to 10C  are diagrams illustrating influence on the developer G caused by the magnetic pole arrangement of the dividing magnetic poles  61 ;  FIG. 10A  is a diagram illustrating a state where the dividing magnetic pole  61  of the first developing roller  42 A is biasedly disposed at the side located further upstream than the dividing magnetic pole  61  of the second developing roller  42 B as in the exemplary embodiment,  FIG. 10B  is a diagram illustrating a state where the dividing magnetic poles  61  are disposed at opposite positions, and  FIG. 10C  is a diagram illustrating a state where the dividing magnetic pole  61  of the first developing roller  42 A is biasedly disposed at the side located further downstream than the dividing magnetic pole  61  of the second developing roller  42 B. 
     The flow of the developer G in such a state is thought to be as follows. Meanwhile, here, the peak values of the normal components of the magnetic flux densities of the dividing magnetic pole  61  of the first developing roller  42 A and the dividing magnetic pole  61  of the second developing roller  42 B are substantially the same as each other. 
     In the magnetic pole arrangement shown in  FIG. 10A , the developer G carried on the second developing roller  42 B is first suctioned by the dividing magnetic pole  61  of the first developing roller  42 A, and a force f1 directed toward the first developing roller  42 A side acts on a great deal of developer G. Thereafter, the developer G is substantially constrained in the meantime due to a suction action f2 of the dividing magnetic poles  61  (N3 pole and S4 pole), and the developer G is separated into both the developing rollers  42 A and  42 B by carrying forces of both the developing rollers  42 A and  42 B. For this reason, the developer G1 and the developer G2 on the first developing roller  42 A and the second developing roller  42 B after division tend to be divided equally. That is, the developer G moves to two places due to f1 and f2, so that the amount of developers (MOS1) attached to the first developing roller  42 A and the amount of developers (MOS2) attached to the second developing roller  42 B tend to be divided equally (MOS1≈MOS2). Meanwhile, when the peak values of the magnetic flux densities of the dividing magnetic poles  61  of two developing rollers  42 A and  42 B are caused to be different from each other, it goes without saying that the division ratio divided equally has a different value, and a great deal of developer G is divided onto the developing roller side having a large peak value. 
     In addition, in the magnetic pole arrangement shown in  FIG. 10B , substantially equal magnetic forces act from both the first developing roller  42 A and the second developing roller  42 B due to both the dividing magnetic pole  61 , and thus the developer G is nipped. Since the developer G is carried by the second developing roller  42 B, the force f1 directed toward the first developing roller  42 A side greatly acts in the opposite locations of two dividing magnetic poles  61 , the developer G1 divided onto the first developing roller  42 A rather tends to increase than the developer G2 on the second developing roller  42 B. That is, a portion of the developer G on the second developing roller  42 B is influenced by the force f1 directed toward the first developing roller  42 A side at positions where two dividing magnetic poles  61  are opposite to each other, and thus the amount of developers (MOS1) attached to the first developing roller  42 A tends to be larger than the amount of developers (MOS2) attached to the second developing roller  42 B (MOS1&gt;MOS2). 
     Further, in the magnetic pole arrangement shown in  FIG. 10C , the developer G held and carried by the second developing roller  42 B is continued to be carried in a state where the developer is suctioned by the dividing magnetic pole  61  of the second developing roller  42 B, and then the influence of the magnetic force of the dividing magnetic pole  61  of the first developing roller  42 A increases. Therefore, the developer G on the second developing roller  42 B is suctioned, the force f1 directed toward the first developing roller  42 A greatly acts, and the developer G is divided onto the first developing roller  42 A. At this time, since much of the developer G on the second developing roller  42 B is suctioned by the dividing magnetic pole  61  of the first developing roller  42 A, the developer G1 on the first developing roller  42 A rather tends to increase than the developer G2 on the second developing roller  42 B. That is, the developer G is first divided at a position on which the dividing magnetic pole  61  of the first developing roller  42 A acts, so that the force f1 directed toward the first developing roller  42 A acts on a portion of the developer G. Therefore, the amount of developers (MOS1) attached to the first developing roller  42 A tends to be larger than the amount of developers (MOS2) attached to the second developing roller  42 B (MOS1&gt;MOS2). 
     In all the states, since the carrying magnetic poles  63  are provided on the downstream side of the dividing magnetic poles  61 , the peeling off of the developer G1 and the developer G2 after division from each of the developing rollers  42 A and  42 B is suppressed, and the developer is carried toward each of the development areas DA and DB in a stable state. 
     Further, in such a state, when the amount of developer G supplied to the opposite locations of the first developing roller  42 A and the second developing roller  42 B changes, that is, when the amount of developer G supplied by changing the speed of the developing roller, for example, in a case of different image sizes is caused to be different, the following estimation is made. Since the developer G moves to only one place (equivalent to f1) in  FIGS. 10B and 10C , the amount of developer G divided depending on the amount of developer G supplied tends to be different, the division ratio tends to change. However, since the developer G moves to two places in  FIG. 10A , the division ratio substantially divided equally is maintained even when the amount of developer G supplied changes. Hence, in the exemplary embodiment, the developer G1 and the developer G2 divided at the division ratio substantially divided equally are carried toward each of the development areas DA and DB. 
     In the exemplary embodiment, the developer G1 on the first developing roller  42 A in the developer G divided in this manner is provided for use in development at the development area DA as shown in  FIG. 6 . Since the first developing roller  42 A rotates in a different direction from that of the photoreceptor  21  at the opposite location, the developer G1 in the development area DA rather strongly hits against the photoreceptor  21 , and thus has a feature of the scattering of magnetic carrier to the photoreceptor  21  side being suppressed. 
     The developer G1 which is held on the first developing roller  42 A and passes through the development area DA is carried with the rotation of the first developing roller  42 A, is peeled off from the first developing roller  42 A due to a repulsion magnetic field between the S2 pole and the S3 pole, and is recovered to the developer carrying path  51  through the guide member  46  (see  FIG. 4 ). 
     On the other hand, as shown in  FIG. 6 , the developer G2 on the second developing roller  42 B after division is provided for use in development at the development area DB. Since the second developing roller  42 B rotates in the same direction as that of the photoreceptor  21  at the opposite location, the developer G2 in the development area DB rather weakly hits against the photoreceptor  21 , and thus has a feature that an obtained toner image is not likely to be disordered. 
     The developer G2 which is held on the second developing roller  42 B and passes through the development area DB is carried with the rotation of the second developing roller  42 B, is peeled off from the second developing roller  42 B due to a repulsion magnetic field acting between the S2 pole and the S3 pole, and is recovered to the developer carrying path  51  side (see  FIG. 4 ). 
     As shown in  FIG. 4 , the developer G1 and the developer G2 which are peeled off from the first developing roller  42 A and the second developing roller  42 B and are recovered to the developer carrying path  51  are stirred and carried by the stirring carrying members  53  and  54  while circulating through two developer carrying paths  51  and  52 , and thus are provided for use in development again as the developer G having a desired amount of electric charge and density. 
     —With Respect to Magnetic Pole Width of Dividing Magnetic Pole and Carrying Magnetic Pole— 
     Next, the magnetic pole widths of the dividing magnetic pole  61  and the carrying magnetic pole  63  will be described.  FIGS. 11A and 11B  are diagrams illustrating magnetic patterns (states where R11, R12, R21 and R22 are normal components of magnetic flux densities and the second developing roller  42 B, not shown, is disposed opposite thereto) of the first developing roller  42 A when the dividing magnetic pole  61  and the carrying magnetic pole  63  having a different magnetic pole width (here, indicated by half-value width) are disposed at the same position;  FIG. 11A  is a diagram illustrating a case where a half-value width θ21 of the carrying magnetic pole  63  is larger than a half-value width θ11 of the dividing magnetic pole  61  (θ21&gt;θ11), and  FIG. 11B  is a diagram illustrating a case where a half-value width θ22 of the carrying magnetic pole  63  is smaller than a magnetic pole width θ12 of the dividing magnetic pole  61  (θ22&lt;θ12). Meanwhile, the angle between a line segment that links a central axis OA of the first developing roller  42 A and a central position of the dividing magnetic pole  61  in the circumferential direction and a line segment that links the central axis OA and a central position of the carrying magnetic pole  63  in the circumferential direction is α+β (see  FIG. 5 ). 
     A relationship between the flow of developer and the half-value width (equivalent to magnetic pole width) in such magnetic patterns is estimated as follows. 
     In  FIG. 11A , the half-value width θ21 of the carrying magnetic pole  63  is caused to be larger than the half-value width θ11 of the dividing magnetic pole  61 . Even when the peak of the tangential component T11 of the magnetic flux density between the dividing magnetic pole  61  and the carrying magnetic pole  63  comes close to the carrying magnetic pole  63  side, the size of the portion (portion indicated by Q in the drawing) in which the normal component of the dividing magnetic pole  61  starts to decrease is sufficiently secured. On the other hand, as shown in  FIG. 11B , when the half-value width θ22 of the carrying magnetic pole  63  is caused to be smaller than the half-value width θ12 of the dividing magnetic pole  61 , the size of the portion (portion indicated by Q in the drawing) in which the normal component of the dividing magnetic pole  61  starts to decrease becomes smaller than in  FIG. 11A , to an extent that the peak of the tangential component T12 of the magnetic flux density between the dividing magnetic pole  61  and the carrying magnetic pole  63  is located at the carrying magnetic pole  63  side. 
     As a result, as shown in  FIG. 11A , when the half-value width of the carrying magnetic pole  63  is caused to be larger than the half-value width of the dividing magnetic pole  61 , the magnetic flux density immediately after division greatly secured, and thus the peeling off of the developer G from the developing roller  42 A after division is further suppressed. Meanwhile, as shown in  FIG. 11B , it goes without saying that the magnetic flux density immediately after division is secured to have a sufficient size as compared to a case where the carrying magnetic pole  63  is not provided. 
     Here, although the half-value widths of the carrying magnetic pole  63  and the dividing magnetic pole  61  are mentioned, the same is true of a case where instead of the half-value width, for example, an angle of occupation (equivalent to zero-point width) on the surfaces of the developing rollers  42 A and  42 B of the normal components of the magnetic flux densities, length in the circumferential direction of a magnet forming a magnetic pole, width having a predetermined ratio (for example, 80%) of the magnetic flux density to the peak value, and the like are indicated. 
     —With Respect to Layout of Carrying Magnetic Pole— 
     Next, a layout of the carrying magnetic pole  63  for the dividing magnetic pole  61  will be described.  FIGS. 12A and 128  are diagrams illustrating magnetic patterns on the first developing roller  42 A side when the installation position of the carrying magnetic pole  63  is changed. Here,  FIG. 12A  is a diagram illustrating a case where the carrying magnetic pole is located approximately midway between the dividing magnetic pole  61  and the developing magnetic pole (not shown), and  FIG. 128  is a diagram illustrating a case where the carrying magnetic pole  63  is disposed more slightly toward the dividing magnetic pole  61  than in  FIG. 12A . 
     In this example, a half-value width θ1 of the dividing magnetic pole  61  and a half-value width θ2 of the carrying magnetic pole  63  are set substantially in the same manner in  FIGS. 12A and 12B , and the half-value width θ1 of the dividing magnetic pole  61  is smaller than the half-value width θ2 of the carrying magnetic pole  63  (θ1&lt;θ2). In addition, the angle between a line segment that links the central axis OA of the first developing roller  42 A and the central position of the dividing magnetic pole  61  in the circumferential direction and a line segment that links the central axis OA and the central position of the carrying magnetic pole  63  in the circumferential direction is set to γ1 in  FIG. 12A , and is set to γ2 in  FIG. 12B  (γ1&gt;γ2). 
     In  FIG. 12A , a tangential component T13 of the magnetic flux density occurs between the dividing magnetic pole  61  and the carrying magnetic pole  63 , due to a normal component R13 of the magnetic flux density of the dividing magnetic pole  61  and a normal component R23 of the carrying magnetic pole  63 . On the other hand, similarly in  FIG. 12B , a tangential component T14 of the magnetic flux density occurs between the dividing magnetic pole  61  and the carrying magnetic pole  63 , due to a normal component R14 of the magnetic flux density of the dividing magnetic pole  61  and a normal component R24 of the carrying magnetic pole  63 . In both the tangential components T13 and T14, in a case where the carrying magnetic pole  63  is brought close to the dividing magnetic pole  61 , the size of the tangential component in the portion (portion indicated by Q in the drawing) in which the normal component of the dividing magnetic pole  61  starts to decrease becomes large to an extent that the peak value of the tangential component comes close to the dividing magnetic pole  61 . For this reason, the carrying property of the developer is more stable in the case in FIG.  12 B. 
     In such magnetic pole arrangement, it is expected that a change occurs due to the size of the half-value width, for example, in a case where the magnetic pole is provided. However, when two developing rollers  42 A and  423  are disposed opposite to each other, it is preferable to bring the carrying magnetic pole  63  close to the dividing magnetic pole  61  side within a range in which the mutual magnetic actions between the heteropolar carrying magnetic poles  63  do not influence each other. Thereby, in the tangential component of the magnetic flux density between the dividing magnetic pole  61  and the carrying magnetic pole  63 , the inclination of a rise from the dividing magnetic pole  61  side increases, and thus the tangential component increases around the dividing magnetic pole  61  to that extent. 
     However, when the carrying magnetic pole  63  is brought excessively close to the dividing magnetic pole  61 , an interaction between the carrying magnetic poles  63  arises, and the tangential component decreases to an extent that the normal component of the magnetic flux density of the carrying magnetic pole  63  increases. Thus, there is a concern that the developer is peeled off from the developing rollers  42 A and  42 B immediately after division. In addition, when the carrying magnetic pole  63  is taken too much away from the dividing magnetic pole  61 , the inclination of a rise from the dividing magnetic pole  61  of the tangential component of the magnetic flux density tends to become gentle, and thus the tangential component in the portion in which the normal component of the dividing magnetic pole  61  starts to decrease becomes small. Hence, it is preferable to bring the carrying magnetic pole  63  close to the dividing magnetic pole  61  within a range beyond the mutual magnetic action between the carrying magnetic poles  63 . 
     In the exemplary embodiment, although an example is shown in which the dividing magnetic poles  61  of the first developing roller  42 A and the second developing roller  42 B are biased toward the upstream side, for example, the dividing magnetic pole  61  on the second developing roller  42 B side may be biased toward the downstream side. Further, the dividing magnetic pole  61  of the first developing roller  42 A may be allowed to be biased toward the upstream side, and the dividing magnetic pole  61  of the second developing roller  42 B may be allowed to be biased toward the downstream side. 
     Further, in the exemplary embodiment, although an example is shown in which the dividing magnetic pole  61  of the first developing roller  42 A is biased toward the side located further upstream than the dividing magnetic pole  61  of the second developing roller  42 B, both the dividing magnetic poles  61  may be disposed at positions opposite to each other, or the dividing magnetic pole  61  of the first developing roller  42 A may be biased toward the side located further downstream than the dividing magnetic pole  61  of the second developing roller  42 B. In the arrangement thereof, the division ratio is not easily divided equally, but it goes without saying that in any case, the carrying of the developer after division is stabilized by including the carrying magnetic pole  63 . 
     In addition, in the exemplary embodiment, although an example is shown in which only the dividing magnetic pole  61  of the first developing roller  42 A is biased toward the upstream side, the carrying magnetic pole  63  of the first developing roller  42 A may be biased toward the upstream side with respect to the carrying magnetic pole  63  of the second developing roller  42 B. Even when both the dividing magnetic pole  61  and the carrying magnetic pole  63  are biased, and the developer G suctioned to the first developing roller  42 A side due to the dividing magnetic pole  61  of the first developing roller  42 A is returned due to the magnetic action of the dividing magnetic pole  61  of the second developing roller  42 B, the size of the tangential component of the magnetic flux density between the dividing magnetic pole  61  and the carrying magnetic pole  63 , in the portion (for example, portion of Q in  FIG. 8B ) in which the normal component of the dividing magnetic pole  61  starts to decrease, is sufficiently secured at the first developing roller  42 A side. Therefore, the amount of developer returned to the second developing roller  42 B side is also reduced, and the division ratio substantially divided equally tends to be maintained. 
     In the exemplary embodiment, although an example is shown in which the photoreceptor  21  rotates (rotates in a clockwise direction in the drawing) in a downward direction in the drawing at an opposite location to the developing device  40 , the photoreceptor  21  is also allowed to rotate in a counterclockwise direction in the drawing. In addition, in the exemplary embodiment, both the first developing roller  42 A and the second developing roller  42 B are configured such that plural V-shaped grooves are formed in the peripheral surfaces thereof. However, the peripheral surface capable of carrying the developer G may be provided, for example, a U-shaped or trapezoidal groove shape may be applied, and the peripheral surface having surface roughness which is set in advance by performing a blasting process using a selected blasting material may be used. 
     Exemplary Embodiment 2 
       FIG. 13  is a partially enlarged view illustrating a developing device  40  of Exemplary Embodiment 2, and is a diagram illustrating a movement of developer G centering on a first developing roller  42 A and a second developing roller  42 B. The developing device  40  of the exemplary embodiment has substantially the same configuration as that in Exemplary Embodiment 1, but the number of magnetic poles of the first developing roller  42 A is five unlike Exemplary Embodiment 1. Meanwhile, the same components as those in Exemplary Embodiment 1 are denoted by the same reference numerals and signs, and the detailed description thereof will be omitted herein. 
     In the exemplary embodiment, the first developing roller  422   k  is disposed at the side close to a developer carrying path, not shown, obliquely upward on the second developing roller  42 B. For this reason, the magnetic pole arrangement within the second developing roller  42 B is the same as that in Exemplary Embodiment 1, but the magnetic pole arrangement within the first developing roller  42 A is different from that in Exemplary Embodiment 1. The first developing roller  42 A is provided with five magnetic poles in the inside thereof. The N2 pole corresponding to a position opposite to the second developing roller  42 B is the dividing magnetic pole  61 , and the S3 pole is the carrying magnetic pole  63 . In addition, the N1 pole is equivalent to the developing magnetic pole  62 , the S1 pole is equivalent to a magnetic pole for peeling, and the S2 pole is equivalent to a magnetic pole that forms a repulsion magnetic field together with the S1 pole. Further, in the exemplary embodiment, similarly to Exemplary Embodiment 1, the dividing magnetic pole  61  (N2 pole) of the first developing roller  42 A to which the developer G is not supplied is biasedly disposed at the side located further upstream than the dividing magnetic pole  61  (S4 pole) of the second developing roller  42 B. 
     In such a configuration, the developer G supplied to the second developing roller  42 B side is divided at an opposite location between the first developing roller  42 A and the second developing roller  42 B due to the magnetic action between the N2 pole of the first developing roller  42 A and the S4 pole of the second developing roller  42 B which are used as the dividing magnetic pole  61 . The divided developer G1 on the first developing roller  42 A is carried by the S3 pole as the carrying magnetic pole  63 , and reaches a development area DA. The developer G1 developed in the development area DA is peeled off from the first developing roller  42 A due to a repulsion magnetic field between the S1 pole and the S2 pole. The peeled developer G1 is recovered to a developer carrying path, not shown, through the guide member  96 . 
     On the other hand, the divided developer G2 on the second developing roller  92 B side is carried toward a development area DB by the S4 pole as the carrying magnetic pole  63 . The developer G2 developed in the development area DB is peeled off from the second developing roller  42 B due to a repulsion magnetic field between the S2 pole and the S3 pole and is recovered to the developer carrying path which is not shown. 
     In this manner, in the exemplary embodiment, since the first developing roller  42 A is disposed obliquely upward on the second developing roller  42 B, the peeling point at which the developer G1 is peeled off from the first developing roller  42 A can be performed at a distant position on the side located further upstream in the direction of rotation of the first developing roller  42 A than a location at which the dividing magnetic pole  61  (N2 pole) is disposed, and thus the number of magnetic poles can be reduced to that extent. The arrangement of the first developing roller  42 A and the second developing roller  42 B is not limited thereto, but, for example, the first developing roller  42 A and the second developing roller  42 B is allowed to be lined up substantially horizontally to each other, and even in this case, the number of magnetic poles of the first developing roller  42 A can be reduced to less than seven. 
     Exemplary Embodiment 3 
       FIG. 14  is a schematic diagram illustrating an outline of a developing device  40  of Exemplary Embodiment 3. The developing device  40  of the exemplary embodiment is substantially the same as that in Exemplary Embodiment 1 with respect to the arrangement of the first developing roller  42 A and the second developing roller  42 B regarding the photoreceptor  21 , but is different from that in Exemplary Embodiment 1, in that a roller to which the developer G is supplied is not the second developing roller  42 B as in Exemplary Embodiment 1, but the first developing roller  42 A disposed upward. Meanwhile, the same components as those in Exemplary Embodiment 1 are denoted by the same reference numerals and signs, and the detailed description thereof will be omitted herein. 
     In the developing device  40  of the exemplary embodiment, the regulation member  45  that regulates the layer thickness of the developer G is provided on the first developing roller  42 A side. In addition, two developer carrying paths  51  and  52  lined up in the vertical direction in the drawing are provided behind the first and second developing rollers  42 A and  42 B in the developing container  41 , and these developer carrying paths  51  and  52  are respectively provided with the stirring carrying members  53  and  54  that stir and carry the developer G. A passage through which the developer G is able to pass between the upper and lower developer carrying paths  51  and  52  is formed on both ends of the two developer carrying paths  51  and  52  in the longitudinal direction, and is configured, for example, such that the developer G in the lower developer carrying path  52  can reach the upper developer carrying path  51  side through the rotation of the lower stirring carrying member  54 . In addition, the permeability-type density sensor  55  is installed on an obliquely downward location of the lower developer carrying path  52 , and is configured such that the toner density of the developer G in the lower developer carrying path  52  is measured. Meanwhile, reference numeral  46  is a guide member that guides the developer G peeled off from the first developing roller  42 A to the developer carrying path  51 . 
     In addition,  FIG. 15  is a partially enlarged view illustrating the developing device  40  of the exemplary embodiment, and is a diagram illustrating a movement of the developer G centering on the first developing roller  42 A and the second developing roller  42 B. In the magnetic pole arrangement of the exemplary embodiment, the dividing magnetic pole  61  (S4 pole) of the second developing roller  42 B which is a developing roller located at the side different from the side to which the developer G is supplied is biasedly disposed at the side located further upstream than the dividing magnetic pole  61  (N3 pole) of the first developing roller  42 A which is a developing roller to which the developer G is supplied. 
     Operations of the developing device  40  having such a configuration will be described with reference to  FIGS. 14 and 15 . 
     In the exemplary embodiment, the developer G having a desired amount of electric charge obtained by stirring in two stirring carrying members  53  and  54  is supplied toward the S2 pole of the first developing roller  42 A with the rotation of the upper stirring carrying member  53 . The layer thickness of the developer G supplied onto the first developing roller  42 A is regulated by the regulation member  45 . In the opposite location between the first developing roller  42 A and the second developing roller  42 B, the developer G held on the first developing roller  42 A is divided onto the first developing roller  42 A side and the second developing roller  42 B side, due to the magnetic action between the N3 pole of the first developing roller  42 A and the S4 pole of the second developing roller  42 B which are used as the dividing magnetic pole  61 . 
     The developer G1 out of the divided the developer G1 and developer G2 on the first developing roller  42 A side is carried toward the development area DA by the S4 pole as the carrying magnetic pole  63 . The developer G1 provided for use in development in the development area DA is carried with the rotation of the first developing roller  42 A, and is peeled off from the first developing roller  42 A due to the action of a repulsion magnetic field between the N2 pole and the N3 pole. The developer G1 peeled off from the first developing roller  42 A is recovered to the developer carrying path  51  by way of the guide member  46 . 
     On the other hand, the developer G2 out of the divided developer G1 and the developer G2 on the second developing roller  42 B side is carried toward the development area DB by the N3 pole as the carrying magnetic pole  63 . The developer G2 provided for use in development in the development area DB is carried with the rotation of the second developing roller  42 B, and is peeled off from the second developing roller  42 B by the action of a repulsion magnetic field between the S2 pole and the S3 pole. The developer G2 peeled off from the second developing roller  42 B is recovered to the lower developer carrying path  52  side as it is. 
     Particularly, in the exemplary embodiment, the dividing magnetic pole  61  of the second developing roller  42 B which is a developing roller to which the developer G is not supplied is biasedly disposed at the side located further upstream than the dividing magnetic pole  61  of the first developing roller  42 A which is a developing roller to which the developer G is supplied. Therefore, similarly to Exemplary Embodiment 1, the developer G1 and the developer G2 supplied to the development area DA and the development area DB tend to be divided at a division ratio substantially divided equally, and a variation in the layer thickness of the developer G1 and the developer G2 after division is also suppressed, thereby allowing an improvement in the uniformity of image quality to be achieved. Meanwhile, in the exemplary embodiment, the direction of rotation of the photoreceptor  21  is also allowed to be set to a reverse direction to the drawing (counterclockwise direction in the drawing). 
     Exemplary Embodiment 4 
       FIG. 16  is a partially enlarged view illustrating a developing device  90  of Exemplary Embodiment 4, and is a diagram illustrating a movement of developer G centering on the first developing roller  42 A and the second developing roller  42 B. The developing device  40  of the exemplary embodiment has substantially the same configuration as that in Exemplary Embodiment 1, but the numbers of carrying magnetic poles  63  of the first developing roller  42 A and the second developing roller  42 B are two, respectively, unlike Exemplary Embodiment 1. Meanwhile, the same components as those in Exemplary Embodiment 1 are denoted by the same reference numerals and signs, and the detailed description thereof will be omitted herein. 
     As magnetic poles within the first developing roller  42 A of the exemplary embodiment, an N1 pole, an S1 pole, an N2 pole, an N3 pole, an S2 pole, an N4 pole, and an S3 pole are provided. The N1 pole is the developing magnetic pole  62 , the S2 pole is the dividing magnetic pole  61 , and the N4 pole and the S3 pole are the carrying magnetic poles  63 . On the other hand, as magnetic poles within the second developing roller  42 B, an S1 pole, an N1 pole, an N2 pole, an S2 pole, an N3 pole, an S3 pole, and an N4 pole are provided. The S1 pole is the developing magnetic pole  62 , the N3 pole is the dividing magnetic pole  61 , and the S3 pole and the N4 pole are the carrying magnetic poles  63 . In the exemplary embodiment, the dividing magnetic pole  61  (S2 pole) of the first developing roller  42 A which is a developing roller to which the developer G is not supplied is biasedly disposed at the side located further upstream than the dividing magnetic pole  61  (N3 pole) of the second developing roller  42 B which is a developing roller to which the developer G is supplied. 
     In such a configuration, the developer G supplied to the second developing roller  42 B side is divided at the opposite location between the first developing roller  42 A and the second developing roller  42 B, due to the magnetic action between the S2 pole of the first developing roller  42 A and the N3 pole of the second developing roller  42 B which are used as the dividing magnetic pole  61 . The divided developer G1 on the first developing roller  42 A is carried by the N4 pole and the S3 pole as the carrying magnetic pole  63 , and reaches the development area DA. The developer G1 developed in the development area DA is peeled off from the first developing roller  42 A due to a repulsion magnetic field between the N2 pole and the N3 pole. The peeled developer G1 is recovered to a developer carrying path, not shown, through the guide member  46 . 
     On the other hand, the divided developer G2 on the second developing roller  42 B side is carried toward the development area DB by the S3 pole and the N4 pole as the carrying magnetic pole  63 . The developer G2 developed in the development area DB is peeled off from the second developing roller  42 B due to a repulsion magnetic field between the N1 pole and the N2 pole and recovered to the developer carrying path which is not shown. 
     In the exemplary embodiment, an example is shown in which two magnetic poles are used as the carrying magnetic pole  63  in both the first developing roller  42 A and the second developing roller  42 B, but, for example, the carrying magnetic pole  63  on one developing roller side may be used as one magnetic pole without being limited thereto, and three or more magnetic poles are allowed to be included as the carrying magnetic pole  63 . In addition, when plural magnetic poles are included as the carrying magnetic pole  63 , when the widths of these magnetic poles are caused to be different from each other, and, for example, the width of the magnetic pole close to the dividing magnetic pole  61  is caused to increase, the tangential component of the magnetic flux density after division is sufficiently secured. 
     Meanwhile, in the example in which two developing rollers  42 A and  42 B are disposed opposite to each other with respect to the photoreceptor  21 , the angle from the dividing magnetic pole  61  to the developing magnetic pole  62 , that is, the angle between a line segment that links the central position of the magnetic pole width along the circumferential direction of the dividing magnetic pole  61  and the rotation center of each of the developing rollers  42 A and  42 B and a line segment that links the central position of the magnetic pole width along the circumferential direction of the developing magnetic pole  62  and the rotation center of each of the developing rollers  42 A and  42 B is generally less than 90 degrees. For this reason, a sufficient magnetic pole width is obtained in the carrying magnetic pole  63 . In addition, in order to simplify the configuration, it is preferable to adopt one magnetic pole as the carrying magnetic pole  63 . 
     Exemplary Embodiment 5 
       FIG. 17  is a schematic diagram illustrating an outline of a developing device  40  of Exemplary Embodiment 5. The developer device  40  of the exemplary embodiment is characterized in that three developing rollers  42 A to  42 C are included with respect to the photoreceptor  21 . The arrangement of the first developing roller  42 A and the second developing roller  42 B are substantially the same as that in Exemplary Embodiment 1, but the developing device  40  is different from the developing device  40  of Exemplary Embodiment 1, in that a third developing roller  42 C is provided as an additional developing roller at the side located further upstream in the direction of rotation of the photoreceptor  21  than the first developing roller  42 A. Meanwhile, the same components as those in Exemplary Embodiment 1 are denoted by the same reference numerals and signs, and the detailed description thereof will be omitted herein. 
     In the developing device  40  of the exemplary embodiment, three developing rollers of the third developing roller  42 C, the first developing roller  42 A, and the second developing roller  42 B are disposed side by side from the upstream side along the direction of rotation of the photoreceptor  21 . The first developing roller  42 A and the second developing roller  42 B rotate similarly to Exemplary Embodiment 1, and the third developing roller  42 C rotates in the same direction as the first developing roller  42 A. That is, in the opposite location to the photoreceptor  21 , the first developing roller  42 A and the third developing roller  42 C rotate in a reverse direction to that of the photoreceptor  21 , and the second developing roller  42 B rotates in the same direction as the photoreceptor  21 . In the exemplary embodiment, in the opposite location between the first developing roller  42 A and the third developing roller  42 C, the developer G1 on the first developing roller  42 A is delivered to the third developing roller  42 C side. 
     In the exemplary embodiment, the regulation member  45  supported by a resin block  47   c  within the developing container  41  is disposed opposite to the second developing roller  42 B. In addition, the guide member  46  extending downward is supported behind the third developing roller  42 C by the resin block  47   c . Meanwhile, it goes without saying that each developing bias is supplied between the three developing rollers  42 A,  42 B, and  42 C and the photoreceptor  21 . 
       FIG. 18  is a diagram illustrating an example of the magnetic pole arrangement within the first developing roller  42 A, the second developing roller  428  and the third developing roller  42 C in the exemplary embodiment, and is a diagram illustrating a flow of developer. 
     The first developing roller  42 A is provided with an N1 pole as the developing magnetic pole  62 , an S1 pole and an S2 pole for peeling off the developer G1, an N2 pole as the dividing magnetic pole  61 , and an S3 pole as the carrying magnetic pole  63 . In addition, the third developing roller  42 C is provided with an S1 pole and N1 pole which are used as the developing magnetic pole  62 , an S3 pole for generating a repulsion magnetic field between the S3 pole and an S2 pole, and an N2 pole and an N3 pole which are provided corresponding to the S1 pole and the S2 pole of the first developing roller  42 A. In addition, in the exemplary embodiment, the dividing magnetic pole  61  (N2 pole) of the first developing roller  42 A is also biasedly disposed at the side located further upstream in the direction of rotation of the first developing roller  42 A than the dividing magnetic pole  61  (S4 pole) of the second developing roller  42 B. Meanwhile, the magnetic pole arrangement of the second developing roller  42 B is the same as that in Exemplary Embodiment 1, and thus the description thereof will be omitted. In addition, in the exemplary embodiment, the circumferential speed of the first developing roller  42 A and the circumferential speed of the third developing roller  42 C are substantially the same as each other. 
     Operations of the developing device  40  having such a configuration will be described with reference to  FIGS. 17 and 18 . 
     In the exemplary embodiment, the developer G having a desired amount of electric charge obtained by stirring in two stirring carrying members  53  and  54  is supplied to the vicinity of the S3 pole of the second developing roller  42 B with the rotation of the stirring carrying member  53 . The layer thickness of the developer G supplied onto the second developing roller  42 B is regulated by the N2 pole as a regulating magnetic pole and the regulation member  45 . In the opposite location between the first developing roller  42 A and the second developing roller  42 B, the developer G of the layer thickness is regulated is divided due to the magnetic action between the N2 pole of the first developing roller  42 A and the S4 pole of the second developing roller  42 B which are used as the dividing magnetic pole  61 , and thus the developer G held on the second developing roller  42 B is divided onto the first developing roller  42 A side and the second developing roller  42 B side. 
     The developer G1 out of the developer G1 and the developer G2 after division on the first developing roller  42 A is carried toward the development area DA by the carrying magnetic pole  63  (S3 pole) in a state where a division ratio is maintained. The developer G1 by which development is completed in the development area DA is carried with the rotation of the first developing roller  42 A. The developer G1 carried onto the first developing roller  42 A is peeled off from the first developing roller  42 A due to the magnetic action between the S1 pole and the S2 pole forming a repulsion magnetic field. At this time, since the third developing roller  42 C is provided with the N3 pole and the N2 pole having a polarity different from that of the 31 pole and the 32 pole, corresponding to the S1 pole and the S2 pole of the first developing roller  42 A, the developer G1 peeled off from the first developing roller  42 A is delivered to the third developing roller  42 C side as it is. That is, in the exemplary embodiment, the magnetic action between the S1 pole and the S2 pole provided on the first developing roller  42 A and the N3 pole and the N2 pole provided on the third developing roller  42 C is equivalent to that in the delivery unit. Meanwhile, the delivery unit is allowed to be other than a system using the above-mentioned repulsion magnetic field, and a well-known system may be adopted. 
     The developer G1 delivered to the third developing roller  42 C is developed in a development area DC, and is carried with the rotation of the third developing roller  42 C. Thereafter, the developer G is peeled off from the third developing roller  42 C due to the magnetic action between the S2 pole and the S3 pole forming a repulsion magnetic field. The developer G1 peeled off from the third developing roller  42 C is recovered to the developer carrying path  51  side by way of the guide member  46 . 
     On the other hand, the developer G2 out of the divided developer G1 and the developer G2 on the second developing roller  42 B side is carried toward the development area DB by the carrying magnetic pole  63  (N3 pole). The developer G2 by which development is completed in the development area DB is carried with the rotation of the second developing roller  42 B, and is peeled off from the second developing roller  42 B due to the magnetic action between the S2 pole and the S3 pole forming a repulsion magnetic field. The developer G2 peeled off from the second developing roller  42 B is recovered to the developer carrying path  51  side. 
     As stated above, in the exemplary embodiment, since development is repeatedly with respect to the electrostatic latent image on the photoreceptor  21 , in three development areas (DC, DA, and DB in order) of the development area DC in the third developing roller  42 C, the development area DA in the first developing roller  42 A, and the development area DB in the second developing roller  42 B, development efficiency for the electrostatic latent image on the photoreceptor  21  is further improved than in a case where the third developing roller  42 C is not included. Further, since the first developing roller  42 A and the second developing roller  42 B are provided with the carrying magnetic poles  63  (equivalent to the S3 pole of the first developing roller  42 A and the N3 pole of the second developing roller  42 B) after division, the developer G1 and the developer G2 in which the variation of layer thickness is suppressed are carried to each development area in a state where a division ratio is stable. 
     In the exemplary embodiment, an example is shown in which the direction of rotation of the photoreceptor  21  is set to a clockwise direction in the drawing, however, the photoreceptor  21  may be set to a reverse direction thereto (counterclockwise direction in the drawing). In this case, in the drawing, the second developing roller  42 B rotates in a reverse direction to that of the photoreceptor  21  in the opposite location to the photoreceptor  21 , and the first developing roller  42 A and the third developing roller  42 C rotate in the same direction as the photoreceptor  21  in the opposite location to the photoreceptor  21 . Even when such a configuration is adopted, the number of development areas formed along with the photoreceptor  21  is three, and thus development efficiency is further improved than in a case where the third developing roller  42 C is not included. 
     Here, although an example is shown in which the third developing roller  42 C is provided with respect to the first developing roller  42 A, the third developing roller  42 C may be provided on the second developing roller  42 B side, and an additional developing roller may be provided on the first developing roller  42 A and the second developing roller  42 B. 
     EXAMPLE 
     Example 1 
     In the present example, in order to confirm the usefulness of the carrying magnetic poles in the first developing roller  42 A and the second developing roller  42 B, magnetic patterns are shown in which seven magnetic poles are included in the insides thereof. Meanwhile, for the purpose of comparison, magnetic patterns of five-pole configurations (first developing roller  42 A′ and second developing roller  42 B′) having no magnetic pole equivalent to the carrying magnetic pole are also shown. 
       FIG. 19  is a diagram illustrating magnetic patterns in the present example. Here, solid lines denote normal components (equivalent to R1 to R7) of magnetic flux densities, and dotted lines denote tangential components (equivalent to T1 to T7) of magnetic flux densities. Here, the magnetic flux density in the simplex of two developing rollers  42 A and  42 B is set to 90 mT in the dividing magnetic pole (magnetic pole equivalent to R1 in the drawing), and is set to 100 mT in the carrying magnetic pole (magnetic pole equivalent to R2 in the drawing). However, even when the magnetic poles having such magnetic flux densities are disposed, the magnetic poles are disposed opposite to each other. Therefore, the normal component (equivalent to R1 in the drawing) of the magnetic flux density at an observed position of the dividing magnetic pole becomes larger than the normal component (equivalent to R2 in the drawing) of the magnetic flux density at a position of the carrying magnetic pole. In addition, the carrying magnetic pole is included next to the dividing magnetic pole, and thus in a tangential component T1 in a location in which the normal component of the magnetic flux density of the dividing magnetic pole falls down, a high value is secured. Meanwhile, it goes without saying that the normal component (equivalent to R3 in the drawing) of the magnetic flux density of the developing magnetic pole becomes larger than the normal component of the magnetic flux density of the dividing magnetic pole disposed opposite thereto. 
     On the other hand,  FIG. 20  is a diagram illustrating magnetic patterns when the number of magnetic poles having no carrying magnetic pole is five, as a comparative example. In this case, since the developing magnetic pole (magnetic pole equivalent to R2 in the drawing) is disposed at a position adjacent to the downstream side of the dividing magnetic pole (magnetic pole equivalent to R1 in the drawing), the tangential component T1 of the magnetic flux density between both becomes small in the vicinity of the dividing magnetic pole due to the influence between the dividing magnetic poles, and is inclined toward the developing magnetic pole. For this reason, the tangential component T1 in a location in which the normal component of the magnetic flux density of the dividing magnetic pole falls down becomes very small, and becomes large when the tangential component comes close to the developing magnetic pole. For this reason, the developer after division tends to be peeled off from the developing rollers  42 A′ and  42 B′. 
     In the present example, since the tangential component (equivalent to T1 in  FIG. 18 ) of the magnetic flux density immediately after division has a high value by providing the carrying magnetic pole between the dividing magnetic pole and the developing magnetic pole, the peeling off of the developer from the developing rollers  42 A and  42 B immediately after division is suppressed, and the developer is stably carried. Thereby, a developer layer in which a fluctuation in a division ratio is suppressed and a fluctuation in the thickness of developer is small is carried to the development area. On the other hand, in the comparative example, since the tangential component of magnetic flux density immediately after division is small, the developer immediately after division tends to be peeled off from the developing rollers  42 A′ and  42 B′, a division ratio tends to fluctuate, and the developer layer of which the thickness tends to fluctuate is carried to the development area. 
     In this case, the same is true of a case where in the division location, the dividing magnetic pole and the carrying magnetic pole of the developing roller different from the developing roller to which the developer is supplied is biasedly disposed at the upstream side, and it goes without saying that the same is true of a case where the width of the carrying magnetic pole is set to be larger than the width of the dividing magnetic pole. 
     Example 2 
     In the present example, as shown in  FIG. 21 , substantially similarly to the configuration of Exemplary Embodiment 1, in an example in which two developing rollers  101  and  102  are lined up vertically inclined by 7 degrees from the vertical direction, and developer G is supplied to the lower developing roller  102 , when the angle of the upper developing roller  101  is changed, that is, when a position relationship between a dividing magnetic pole and a carrying magnetic pole in the upper and lower developing rollers  101  and  102  is changed, it is confirmed what the division ratio of the developer is. Here, the dividing magnetic pole is set to x1 and x2, and the carrying magnetic pole is set to y1 and y2. Meanwhile, reference numeral  100  is a photoreceptor. 
     In such a configuration, evaluation is made under the following conditions.
         Half-value width of dividing magnetic poles x1 and x2: constant (here, 20 degrees)   Magnetic flux density of dividing magnetic poles x1 and x2: 90 mT (simplex)   Half-value width of carrying magnetic poles y1 and y2: two levels of 30 degrees and 20 degrees   Magnetic flux density of carrying magnetic poles y1 and y2: 100 mT (simplex)   Circumferential speeds v1 and v2 of developing roller: v1≈v2       

     In addition, the developer G is supplied from the lower developing roller  102  side, and the amount of developer supplied is set to two levels (low MOS, high MOS: mass On Sleeve) by changing a gap between the regulation member and the roller. Further, the angle (referred to as an upper MSA: MSA=Magroll Set Angle) is changed in the rotation direction centering on a central axis O1 of the upper developing roller  101 . At this time, in the present example, when the lower developing roller  102  is installed, the position of a dividing magnetic pole β2 of the lower developing roller  102  deviates to the side located five degrees further upstream than a line segment that links the central axis O1 of the upper developing roller  101  and a central axis O2 of the lower developing roller  102 , but confirmation is made in this state. 
     As an evaluation content, each of the amounts of developer attached (referred to as upper MOS and lower MOS) on the upper developing roller  101  and the lower developing roller  102  after the developer G is divided is obtained, and the ratio thereof (upper MOS/lower MOS) is calculated. A result based on such conditions when the half-value width of the carrying magnetic poles y1 and y2 is 30 degrees is shown in  FIG. 22 , and a result when the half-value width of the carrying magnetic poles y1 and y2 is 20 degrees is shown in  FIG. 23 . 
     From  FIG. 21 , the following points are confirmed.
         The rotation of the upper MSA toward the developing container (HSG) side, that is, the biasing of the magnetic poles x1 and y1 of the upper developing roller  101  toward the upstream side tend to set the division ratio of the developer to 1:1.   When the upper MSA is rotated toward the photoreceptor (PR) side, that is, the magnetic poles x1 and y1 of the upper developing roller  101  is biased toward the downstream side, a great deal of developer is divided onto the upper developing roller  101  side, and when the angle of rotation is slightly changed, the division ratio is changed.   Even when the amount of developer supplied is changed, a relationship between the upper MSA and the division ratio transitions substantially similarly.   In order to set the division ratio to substantially 1:1 even when the amount of developer supplied is changed, the upper developing roller  101  is preferably rotated 2 to 6 degrees toward the developing container side.       

     From  FIG. 22 , the following points are confirmed.
         The rotation of the upper MSA toward the developing container (HSG) side, that is, the biasing of the magnetic poles x1 and y1 of the upper developing roller  101  toward the upstream side tend to set the division ratio of the developer to 1:1.   When the upper MSA is rotated toward the photoreceptor (PR) side, that is, the magnetic poles x1 and y1 of the upper developing roller  101  is biased toward the downstream side, a greater deal of developer is divided onto the upper developing roller  101  rather than when the half-value width of the carrying magnetic pole is 30 degrees, and the division ratio is greatly changed only by changing the angle of rotation slightly.   When the amount of developer supplied is caused to increase, the amount of increase in the developer of the upper developing roller  101  decreases further than when the amount of developer supplied is caused to decrease.   In order to set the division ratio to substantially 1:1 even when the amount of developer supplied is changed, the upper developing roller  101  is preferably rotated 4 to 9 degrees toward the developing container side.       

     From the above, it is understood that the half-value width (equivalent to magnetic pole width) of 20 degrees of the carrying magnetic pole can stabilize the division ratio than that of 30 degrees. 
     Further, the inventor has confirmed that as a result of performing the same evaluation as that in the present example by changing the peak value of the magnetic flux density of the mutual dividing magnetic pole in two developing rollers, the developer is divided with a similar tendency though the division ratios are different from each other. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.