Patent Publication Number: US-10761473-B2

Title: Developing device capable of suppressing the passing of a relatively large amount of developer and image forming apparatus therewith

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2018-180689 filed Sep. 26, 2018. 
     BACKGROUND 
     (i) Technical Field 
     The present disclosure relates to a developing device and an image forming apparatus. 
     (ii) Related Art 
     Examples of known related-art techniques such as developing devices and image forming apparatuses that suppress the occurrences of problems caused by flying toner (toner cloud) include the following. 
     For example, a developing device is described in Japanese Unexamined Patent Application Publication No. 9-54494. This developing device includes a sealing device that seals developer dropping from a developing roller. The sealing device includes a sealing member that is disposed below the developing roller and extends along the entirety of the developing roller in the axial direction. When the developing roller is at a developing position, the distance between the sealing member and the surface of a photoconductor is uniform. 
     Also, an image forming apparatus is described in Japanese Unexamined Patent Application Publication No. 8-190265. This image forming apparatus includes a photoconductor drum, a developing roller, and a transfer roller. The developing roller is rotated such that a portion of the developing roller closest to the photoconductor drum is moved in the same direction as that of the photoconductor drum so as to form a toner image. The transfer roller transfers the toner image on the photoconductor drum to a transfer receiving member. The image forming apparatus has an opening that is elongated in the axial direction of the photoconductor drum and disposed between the developing roller and the transfer roller so as to be close to the photoconductor drum and face upward. The image forming apparatus includes a toner cloud discharge duct that extends downward or obliquely downward. The width of the opening of the toner cloud discharge duct in the rotating direction of the photoconductor drum is larger than the distance between an end portion of the opening near the transfer roller and the surface of the photoconductor drum. 
     Also, an image forming unit is described in Japanese Unexamined Patent Application Publication No. 2015-79134. This image forming unit includes a developing member, a housing member, and a guide member. The developing member develops an electrostatic latent image formed on an image holding body being rotated. The housing member has an end portion that faces an image holding body at a portion downstream of the developing member in a moving direction of the image holding body and houses the developing member. The guide member faces the end portion at a portion downstream of the housing member in the moving direction of the image holding body and guides a recording medium toward the image holding body. A channel is formed between the end portion of the housing member and the guide member. The channel directs an airflow generated by rotation of the image holding body in a direction separating from the image holding body. 
     Also, a toner cloud collecting device is described in Japanese Patent No. 3467943. This toner cloud collecting device is disposed close to a developing device in which developer that includes at least toner is contained in a developing housing having a developing opening. The toner cloud collecting device collects a toner cloud flowing out through the developing opening. 
     According to Japanese Patent No. 3467943, the toner cloud collecting device includes a cloud collecting housing, a suction applying device, and a suction distribution setting device. The duct-shaped could collecting housing has a cloud collecting opening. The suction applying device applies a suction to the toner cloud from the cloud collecting opening toward the inside of the cloud collecting housing. The suction distribution setting device sets the suction such that, in the cloud collecting opening, a suction to the toner cloud is larger at a portion corresponding to a region other than a passing region of a transfer medium of a preset reference size than that at another portion. A blower device serving as the suction applying device is disposed in a duct serving as the cloud collecting housing or a communicating portion of the duct. Meanwhile, an airflow amount adjusting member serving as the suction distribution setting device is provided near the cloud collecting opening of the duct serving as the cloud collecting housing. This airflow amount adjusting member has a plurality of gaps for adjusting the amount of airflow passing therethrough. The size of the gaps is set to be larger at the portion corresponding to the region other than the passing region of the transfer medium of the reference size than that at the other region. 
     SUMMARY 
     Aspects of non-limiting embodiments of the present disclosure relate to a developing device and an image forming apparatus including this developing device. When, out of an airflow generated by rotation of a developer holding device, part of the airflow that does not flow to an inside of a housing is introduced into and passes through, together with part of developer included in the airflow and flying, a through portion disposed at a portion of the housing including a downstream edge portion of a developing opening, this developing device is able to suppress passing or existing of relatively large amount of the developer through or in both end regions of the through portion in an axial direction of the developer holding device. 
     Aspects of certain non-limiting embodiments of the present disclosure overcome the above disadvantages and/or other disadvantages not described above. However, aspects of the non-limiting embodiments are not required to overcome the disadvantages described above, and aspects of the non-limiting embodiments of the present disclosure may not overcome any of the disadvantages described above. 
     According to an aspect of the present disclosure, there is provided a developing device including a housing, a developer holding device, and a directing device. The housing includes a container portion containing developer and has a developing opening. The developer holding device holds the developer in the container portion of the housing and is rotated so as to pass the developing opening. The developing device has a through portion disposed at a portion of the housing including a downstream edge portion at a downstream portion of the developing opening in a direction in which the developer holding device is rotated. The through portion has an inlet, an outlet, and a passage that connects the inlet and the outlet to each other so as to allow part of an airflow generated by rotation of the developer holding device to be introduced thereinto and flow therethrough. The directing device extends from a portion of the housing opposite to the developing opening with the inlet of the through portion interposed therebetween toward the developer holding device so as to direct the part of the airflow toward the inlet. In an axial direction of the developer holding device, an opening area of a portion of the inlet of the through portion disposed in a central region is larger than a total of opening areas of portions of the inlet of the through portion disposed in end regions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present disclosure will be described in detail based on the following figures, wherein: 
         FIG. 1  is an overview illustrating the entirety of an image forming apparatus according to a first exemplary embodiment; 
         FIG. 2  is an enlarged overview of part (image making device including the developing device) of the image forming apparatus illustrated in  FIG. 1 ; 
         FIG. 3  is a schematic sectional view of the developing device used for the image forming apparatus illustrated in  FIG. 1 ; 
         FIG. 4  is an overview of part of the developing device (with a directing device omitted) illustrated in  FIG. 3 ; 
         FIG. 5  is an overview of the structure of an inlet of a through portion of the developing device illustrated in  FIG. 5 ; 
         FIG. 6  is an enlarged schematic sectional view of the structure of part of the developing device; 
         FIG. 7A  is a schematic sectional view of a state of operation of the developing device, and  FIG. 7B  is a schematic sectional view of a next state of the operation of the developing device; 
         FIG. 8A  is a schematic sectional view of a state of operation of the developing device illustrated in  FIG. 3 , and  FIG. 8B  is a schematic sectional view of a next state of the operation of this developing device; 
         FIG. 9  is a conceptual view illustrating the relationship between a developed state of the through portion and a passing sheet of paper; 
         FIGS. 10A and 10B  illustrate a developing device according to a second exemplary embodiment, and out of  FIGS. 10A and 10B ,  FIG. 10A  is a schematic sectional view of the structure of the developing device, and  FIG. 10B  is a schematic sectional view of a state of operation of this developing device; 
         FIG. 11  is a schematic sectional view of the structure of a developing device according to a third exemplary embodiment; 
         FIG. 12  is an overview of part of the developing device (with the directing device omitted) illustrated in  FIG. 11 ; 
         FIG. 13  is a conceptual view of the structure and an operating state of a through portion of the developing device illustrated in  FIG. 11  with the through portion developed; 
         FIG. 14  is a conceptual view of the structure and an operating state of a through portion of a developing device according to a fourth exemplary embodiment with the through portion developed; 
         FIG. 15  is an overview of another example of the structure of the inlet of the through portion; 
         FIG. 16  is an overview of yet another example of the structure of the inlet of the through portion; 
         FIG. 17  is an overview of yet another example of the structure of the inlet of the through portion; and 
         FIG. 18  is an overview of the other structure of the inlet of the through portion. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present disclosure will be described below with reference to the drawings. 
     First Exemplary Embodiment 
       FIGS. 1 to 3  illustrate a first exemplary embodiment of the present disclosure.  FIG. 1  illustrates the structure of an image forming apparatus  1  that includes a developing device according to the first exemplary embodiment.  FIG. 2  is an enlarged view of part (image making device including the developing device) of the image forming apparatus  1 .  FIG. 3  is an enlarged view of the structure of the developing device used for the image forming apparatus  1 . 
     Overall Structure of the Image Forming Apparatus 
     The image forming apparatus  1  is a printer as an example of an image forming apparatus. The image forming apparatus  1  forms images formed by developer (toner) on sheets of pater  9 . The images are formed based on image information that is input from the outside and includes all or a subset of characters, photographs, graphics, and the like. 
     As illustrated in  FIG. 1 , the image forming apparatus  1  includes an image making device  2 , a sheet feed device  3 , a fixing device  4 , and so forth disposed in a housing  10  serving as an apparatus body. The image making device  2  forms toner images including the toner as the developer by using an electrophotographic system or the like and transfers the toner images onto the sheets  9 . The sheet feed device  3  contains the required sheets  9  and supplies the sheets  9  to a transfer position of the image making device  2 . The fixing device  4  fixes the toner images transferred onto the sheets  9 . 
     The housing  10  includes various members such as structural members, exterior members, and so forth. An output receiving unit  11  that receives the sheets  9  on which the images have been formed and which is output is provided in an upper portion of the housing  10 . The output receiving unit  11  has a receiving surface including an inclined surface provided below an output opening  12  provided in the housing  10 , thereby receiving the sheets  9  output from the output opening  12 . 
     As illustrated in  FIGS. 1 and 2 , the image making device  2  includes a charger  22 , a light exposure device  23 , a developing device  5 , a transfer device  25 , a cleaner  26 , and so forth arranged in this order around a photoconductor drum  21  that is to be driven so as to be rotated in an arrow A direction. 
     Out of these, the charger  22  is of a contact charging type or the like and charges a circumferential surface of the photoconductor drum  21  (an outer circumferential surface portion to serve as an image forming region) to a required polarity and a required potential. The light exposure device  23  forms on the charged circumferential surface of the photoconductor drum  21  electrostatic latent images by radiating light corresponding to image information (signals) input to the image forming apparatus  1  by a various method. The developing device  5  develops the electrostatic latent images on the photoconductor drum  21  so as to form toner images by supplying the toner as the developer. The transfer device  25  is of a contact transfer type or the like and electrostatically transfers the toner images on the photoconductor drum  21  onto the sheets  9 . The cleaner  26  cleans the circumferential surface of the photoconductor drum  21  by removing unnecessary matter such as residual toner attracted to the circumferential surface of the photoconductor drum  21 . 
     The details of the developing device  5  will be described later. 
     The sheet feed device  3  is disposed at a position separated from the image making device  2  toward a lower portion in the direction of gravity. The sheet feed device  3  includes sheet containers  31 , a feed device  33 , and so forth. The sheet containers  31  each contain a plurality of the sheets  9  of a required size, type and so force used for forming images. The plurality of sheets  9  contained in the sheet container  31  are stacked one on top of another on a placement plate  32 . The feed device  33  feeds one sheet after another from the sheets  9  contained in the sheet container  31 . 
     The sheet container  31  is attached to the housing  10  such that the sheet container  31  is able to be drawn out from the housing  10 . A plurality of the sheet containers  31  are provided in accordance with the forms of application. It is sufficient that the sheets  9  be recording media that are able to be transported in the housing  10  and that allow the toner images to be transferred and fixed thereto. For example, normal paper, coated paper, cardboards, postcards, or the like cut into a predetermined size or envelopes are used. 
     The fixing device  4  is disposed at a position separated substantially horizontally (in a direction substantially parallel to the coordinate axis X) from the image making device  2 . The fixing device  4  includes a heating rotating body  41 , a pressure rotating body  42 , and so forth. The heating rotating body  41  and the pressure rotating body  42  are disposed in a housing  40  having an introduction opening and an exit opening, in contact with each other, and to be rotated. 
     The heating rotating body  41  is a heating fixing member in the form of a roller, a belt, or the like. The heating rotating body  41  is, as illustrated in  FIG. 1 , rotated in an arrow direction. The heating rotating body  41  is heated by a heating device (not illustrated) such that the temperature of an outer circumferential surface thereof is maintained at a required temperature. The pressure rotating body  42  is a pressure-applying fixing member in the form of a roller, a belt, or the like. The pressure rotating body  42  is in contact with the heating rotating body  41  along a substantially axial direction of the heating rotating body  41  at a required pressure, thereby being rotated. Furthermore, in the fixing device  4 , a portion where the heating rotating body  41  and the pressure rotating body  42  are in contact with each other is a fixing processing portion FN where the sheets  9  onto which unfixed toner images have been transferred pass through so as to be subjected to required fixing processing (such as heating, applying pressure, and so forth). 
     Furthermore, as illustrated by two-dot chain lines Rt in  FIG. 1 , the image forming apparatus  1  has sheet transport paths through which each of the sheets  9  is typically transported in the housing  10 . 
     The typical sheet transport paths include, for example, a supply transport path Rt 1 , a relay transport path Rt 2 , an output transport path Rt 3 , and a duplex transport path Rt 4 . The supply transport path Rt 1  is provided between the feed device  33  of the sheet feed device  3  and a transfer position TP (a position where the photoconductor drum  21  and the transfer device  25  face each other) of the image making device  2 . The relay transport path Rt 2  is provided between the transfer position TP of the image making device  2  and the fixing processing portion FN of the fixing device  4 . The output transport path Rt 3  is provided between the fixing processing portion FN of the fixing device  4  and the output receiving unit  11  of the housing  10 . The duplex transport path Rt 4  is provided between an end (branching portion) of the output transport path Rt 3  and a middle position (merging portion) of the supply transport path Rt 1 . 
     Out of these transport paths, the supply transport path Rt 1  is formed by using a plurality of transport roller pairs  34   a ,  34   b ,  34   c , a plurality of transport guide members (not illustrated), and so forth to generally have a U shape turned substantially sideways. The transport roller pair  34   c  is a so-called registration roller pair that starts to be rotated at timing adjusted to transfer timing so as to feed the sheet  9  toward the transfer position TP of the image making device  2 . 
     Furthermore, the supply transport path Rt 1  is disposed so as to pass through a position below the developing device  5  in the direction of gravity upstream of the transfer position TP of the image making device  2  in the direction in which the sheet  9  is transported. At this time, in the supply transport path Rt 1 , a transport guide member  13  that guides a non-transfer surface (back side) of the sheet  9  may be disposed below the developing device  5  in the direction of gravity as exemplified in  FIG. 2 . 
     The relay transport path Rt 2  is formed by using a plurality of transport guide members (not illustrated) so as to entirely extend in a generally horizontal direction. 
     The output transport path Rt 3  is formed by using a plurality of transport roller pairs  35   a ,  35   b ,  36  and a plurality of transport guide members (not illustrated) to generally have a shape that extends upward while being curved. The transport roller pair  36  is an output roller pair that is provided immediately upstream of the output opening  12  in the direction in which the sheet  9  is transported and feeds the sheet  9  having undergone fixing to the output receiving unit  11 . 
     The duplex transport path Rt 4  includes the transport roller pair  36 , a plurality of transport roller pairs  37   a ,  37   b ,  37   c ,  37   d , a route switching member (not illustrated), a plurality of transport guide members (not illustrated), and so forth. The transport roller pair  36  serving as the output roller pair is the end of the output transport path Rt 3  and rotatable in the normal and reverse directions. The route switching member switches the destination of the route of the sheet  9 . 
     Image Forming Operation Performed by the Image Forming Apparatus 
     The image forming apparatus  1  forms images as follows. Here, the image forming operation is described with an example of a basic simplex image forming operation performed when an image is formed on one side of the sheet  9 . 
     In the image forming apparatus  1 , the image making device  2 , the sheet feed device  3 , the fixing device  4 , and so forth start up when, for example, a controller (not illustrated) receives a request instruction (signal) for the image forming operation from an external information terminal or the like connected through various communication devices. 
     Initially, operations for forming an image is performed in the image making device  2 . First, the photoconductor drum  21  starts rotation, and the charger  22  charges the circumferential surface of the photoconductor drum  21  to a specified polarity (negative polarity in the present example) and a specified potential. Then, the light exposure device  23  causes the charged circumferential surface of the photoconductor drum  21  to be exposed to light in accordance with the image information so as to form an electrostatic latent image including required patterns. After that, the developing device  5  performs developing by supplying the toner serving as the developer charged to a required polarity (negative polarity according to the present example) toward the electrostatic latent image formed on the circumferential surface of the photoconductor drum  21 , thereby making the electrostatic latent image visible as a toner image formed by the toner. Thus, the toner image is formed on the photoconductor drum  21 . 
     Next, in the image making device  2 , the photoconductor drum  21  being rotated transports the toner image to the transfer position TP facing the transfer device  25 . Meanwhile, in the sheet feed device  3 , the sheet  9  is fed to the supply transport path Rt 1  at timing adjusted to this transfer timing so as to be supplied to the transfer position TP of the image making device  2 . At the transfer position TP of the image making device  2 , the transfer device  25  forms a transfer electric field so as to electrostatically transfer the toner image on the photoconductor drum  21  onto the one side of the sheet  9 . Furthermore, in the image making device  2 , the cleaner  26  continues to clean the circumferential surface of the photoconductor drum  21  at a time including a time after this transfer. 
     Next, the sheet  9  onto which the toner image has been transferred is fed to the relay transport path Rt 2  while being pinched between the photoconductor drum  21  being rotated and the transfer device  25  and subjected to a transport force so as to be transported to the fixing device  4 . In the fixing device  4 , the sheet  9  is introduced into and passes through the fixing processing portion FN between the heating rotating body  41  driven to be rotated in the arrow direction and the pressure rotating body  42  rotated by following the heating rotating body  41 . When the sheet  9  passes through the fixing processing portion FN, the toner of the toner image on the one side of the sheet  9  is heated and fused under pressure so as to be fixed onto the sheet  9 . 
     At last, the sheet  9  having undergone the fixing is fed from the fixing processing portion FN of the fixing device  4  to the output transport path Rt 3  and transported. After that, the sheet  9  is output from the output opening  12  of the housing  10  by the transport roller pair  36 , thereby finally being received in the output receiving unit  11 . 
     Thus, a monochrome image formed of the toner of a single color is formed on the one side of a single sheet  9 , and the simplex image forming operation is completed. When an instruction for performing the image forming operation on a plurality of the sheets  9  is issued, the above-described series of operations are similarly repeatedly performed as many times as the number of the sheets  9 . 
     Furthermore, in a duplex printing operation for forming images on both the front and back sides of the sheet  9 , the sheet  9  onto one side (first side: front side) of which the transferred toner image has been fixed is fed to the duplex transport path Rt 4  after the above-described simplex image forming operation has been similarly performed. 
     In so doing, the sheet  9  onto the one side of which the toner image has been fixed is stopped in a state in which a leading end portion of the sheet  9 , the leading end portion being at the leading end when the sheet  9  is transported, is temporarily output from the output opening  12  while being pinched between the transport roller pair  36 . Then, by a displacement operation of the route switching member for switching the route and reverse rotating operation of the output roller pair  36 , the sheet  9  is fed to the duplex transport path Rt 4  first from a trailing end portion, the trailing end portion being at the trailing end when the sheet  9  transported. 
     Next, the sheet  9  having fed to the duplex transport path Rt 4  is transported through the duplex transport path Rt 4 . Then, the sheet  9  is transported through a path that merges with the supply transport path Rt 1  at a position of the supply transport path Rt 1  upstream of the transport roller pair  34   b  in the sheet  9  transport direction. Thus, the sheet  9  having been inverted is fed to the supply transport path Rt 1 . 
     Finally, as is the case with the simplex image forming operation, the sheet  9  fed again to the supply transport path Rt 1  is fed to the transfer position TP of the image making device  2  at the transfer timing, and a toner image is transferred onto the other side (second side: back side) of this sheet  9 . After that, the sheet  9  is transported to the fixing device  4  and the toner image is fixed. At last, the sheet  9  on both the front and back sides of which the images have been formed is transported through the output transport path Rt 3  similarly to the above-described case, and then output to and received in the output receiving unit  11 . 
     Thus, monochrome images formed of the toner of a single color are respectively formed on the front and back sides of a single sheet  9 , and the duplex image forming operation is completed. 
     Structure of the Developing Device 
     Next, the developing device  5  is described. 
     As illustrated in, for example,  FIGS. 2 and 3 , the developing device  5  includes a housing  50  that houses the elements disposed therein. Typically, elements such as a developing roller  53 , a layer thickness regulating member  54 , and two agitating transport members  55 ,  56  are disposed in the housing  50 . 
     The entirety of the housing  50  has an external shape elongated in one direction. The housing  50  has, as illustrated in, for example,  FIG. 3 , a container portion  51 , a developing opening  52 , and so forth. The container portion  51  contains developer  15 . The developing opening  52  opens a portion of the container portion  51  facing the photoconductor drum  21 . 
     The housing  50  is separable into, for example, a body portion (housing lower portion) included in a lower structure of the housing  50  and a lid portion (housing upper portion) that closes an upper side of the housing  50  and is included in an upper structure of the housing  50 . As the developer  15 , so-called two-component developer that includes non-magnetic toner including fine powder colored with a desired color (such as black) and magnetic carrier including magnetic particles is used. 
     The container portion  51  of the housing  50  has two transport paths  51   a ,  51   b  (a first transport path  51   a  and a second transport path  51   b ) parallel to the axial direction of the developing roller  53 . 
     The two transport paths  51   a ,  51   b  are parallel to each other and linearly extend in the longitudinal direction of the housing  50 . The two transport paths  51   a ,  51   b  are in such a positional relationship in which the two transport paths  51   a ,  51   b  are disposed at slightly different positions in the up-down direction. Furthermore, central portions of the two transport paths  51   a ,  51   b  adjacent to each other are separated from each other by a separator wall. In contrast, the two transport paths  51   a ,  51   b  are connected to each other at connecting portions without separator wall at upstream end portions and downstream end portions in the transport direction of the two transport paths  51   a ,  51   b . Thus, the two transport paths  51   a ,  51   b  form in combination a circulating path structure. Furthermore, out of the two transport paths  51   a ,  51   b , the first transport path  51   a  close to the developing roller  53  is typically used as a supply transport path through which the developer  15  is supplied to the developing roller  53 , and the second transport path  51   b  far from the developing roller  53  is typically used as a mixing transport path in which the developer  15  contained therein is mixed with newly replenished toner or the like. 
     The developing opening  52  allows part of the developing roller  53  to be exposed to the outside so as to perform the developing step. For this purpose, the developing opening  52  has, for example, a rectangular shape having a slightly larger dimension than that of an effective image forming region in the direction of the axis of rotation of the photoconductor drum  21 . Reference numeral  57  in  FIG. 3  denotes a leakage suppressing member, that is, a so-called sealing member that suppresses leakage of the developer  15  (typically, toner) through a gap between the developing device  5  and the photoconductor drum  21  and a gap between the developing opening  52  of the housing  50  and the developing roller  53 . 
     The developing roller  53  holds at the outer circumferential surface thereof the developer  15  in the container portion  51  by a magnetic force and transports the held developer  15  to a surface portion DE serving as a developing performing region facing the outer circumferential surface of the photoconductor drum  21  with a required gap therebetween. The developer  15  transported to the surface portion DE passes through the surface portion DE. The developing performing region is a region having a predetermined width through the center of which a line CL ( FIG. 2 ) connecting a center point of rotation  01  of the developing roller  53  and a center point of rotation  02  of the photoconductor drum  21  passes, or a region where a magnetic force of a developing magnetic pole disposed in a magnet roller ( 532 ) of the developing roller  53 , which will be described later, effectively works. 
     As illustrated in  FIG. 3 , the developing roller  53  includes a sleeve  531  and the magnet roller  532 . The sleeve  531  is an example of a cylindrical member provided so as to be rotated while partially being exposed from the developing opening  52  in the housing  50 . The magnet roller  532  is an example of a magnet member secured in a cylindrical space of the sleeve  531 . 
     The sleeve  531  is a cylindrical member formed of a non-magnetic material such as stainless steel or aluminum. For example, the sleeve  531  is mounted such that, as illustrated in  FIG. 4 , shaft portions  531   a ,  531   b  provided at respective ends of the sleeve  531  are rotatably mounted at mounting portions  50   c  provided at a side wall of the housing  50  with bearings  535  or the like interposed therebetween. Furthermore, for example, a gear  537  is mounted on the shaft portion  531   a  being one of the shaft portions  531   a ,  531   b . This gear  537  receives rotational motive power transmitted from a rotational drive device (not illustrated) through a gear train or the like so as to rotate the sleeve  531  in an arrow C direction. Furthermore, a developing voltage is supplied from a power source (not illustrated) to a region between the sleeve  531  and the photoconductor drum  21 . 
     Meanwhile, the magnet roller  532  has a structure in which, as illustrated in  FIG. 6 , a plurality of magnetic poles (south poles and north poles) are disposed at predetermined positions. These magnetic poles generate magnetic forces that cause the particles of the magnetic carrier of the developer  15  to be attracted so as to form a magnetic brush in which the particles of the magnetic carrier are continuously disposed to form a chain shape along magnetic lines of force on the outer circumferential surface of the sleeve  531 . Referring to  FIG. 6 , reference numeral S 1  denotes a developing magnetic pole, reference numeral N 1  denotes a removing magnetic pole, reference numeral N 2  denotes an attracting magnetic pole, reference numeral S 2  denotes a layer thickness adjusting magnetic pole, and reference numeral N 3  denotes a transport magnetic pole. 
     The magnet roller  532  is mounted such that, for example, shaft portions of the magnet roller  532  projecting from respective ends of the magnet roller  532  pass through respective inner spaces of the shaft portions  531   a ,  531   b  of the sleeve  531  and are secured to the respective mounting portions  50   c  on the side wall of the housing  50 . 
     The layer thickness regulating member  54  regulates the thickness of a layer of the developer  15  (magnetic brush) held on the sleeve  531  of the developing roller  53  such that the layer thickness is maintained at a substantially uniform thickness. 
     The layer thickness regulating member  54  is mounted so as to be secured to a mounting portion formed in the housing  50  such that the layer thickness regulating member  54  is kept separated from the outer circumferential surface of the sleeve  531  of the developing roller  53  with a required gap (regulating gap) corresponding to the layer thickness required for the developer  15  set therebetween and the layer thickness regulating member  54  is maintained in a state in which the layer thickness regulating member  54  and the sleeve  531  face each other along an axial direction D of the rotation shaft (shaft portion) of the sleeve  531 . For example, a cylindrical member having a length larger than or equal to the length of an effective developing region in the axial direction of the developing roller  53  (sleeve  531 ) is used for the layer thickness regulating member  54 . More specifically, this cylindrical member is formed of a non-magnetic material such as, for example, stainless steel. Furthermore, the layer thickness regulating member  54  is disposed upstream of (above) the center of rotation of the developing roller  53  (the center of rotation of the shaft portion  531   a  of the sleeve  531  or the like) in the direction of gravity. 
     As illustrated in, for example,  FIGS. 2 and 3 , the two agitating transport members  55 ,  56  are separately disposed in the first transport path  51   a  and the second transport path  51   b  of the housing  50  and transport the developer  15  contained in the respective transport paths  51   a ,  51   b  in the required directions (transport directions of the transport paths  51   a ,  51   b ) while agitating the developer  15 . 
     For each of the agitating transport members  55 ,  56 , a structure in which a plate-shaped transport portion  55   b ,  56   b  is spirally wound on a circumferential surface of a rotation shaft  55   a ,  56   a  (so-called screw auger) is used. Furthermore, both end portions of the rotation shaft  55   a ,  56   a  of each of the agitating transport members  55 ,  56  are rotatably mounted on bearings (not illustrated) provided on the side wall surface of the housing  50 . Furthermore, a gear (not illustrated) is mounted on one end portion of the rotation shaft  55   a ,  56   a  of each of the agitating transport members  55 ,  56 , thereby the agitating transport member  55 ,  56  is rotated in a required direction by receiving the rotational drive power distributed from the developing roller  53  (sleeve  531 ). 
     Basic Operation of the Developing Device 
     In the developing device  5  having the above-described structure, when time of operation such as the image forming operation by the image forming apparatus  1  comes, the sleeve  531  of the developing roller  53  and the agitating transport members  55 ,  56  start to be rotated and the developing voltage is supplied to the developing roller  53  and the sleeve  531 . 
     Thus, the two-component developer  15  contained in the container portion  51  of the housing  50  is transported in the predetermined directions through the first transport path  51   a  and the second transport path  51   b  of the container portion  51  while being agitated by the rotating agitating transport members  55 ,  56  and transported so as to be moved at the end portions for transportation in the transport paths  51   a ,  51   b  to the other transport paths  51   b ,  51   a  through the connecting portions (not illustrated). Thus, the developer  15  is transported so as to be circulated in a single direction when the entirety of the container portion  51  is seen. In so doing, the non-magnetic toner of the developer  15  and the magnetic carrier of the developer  15  are sufficiently agitated, and the non-magnetic toner is triboelectrically charged and electrostatically attracted to the surfaces of the magnetic carrier. 
     Next, part of the developer  15  transported by the agitating transport member  55  disposed close to the developing roller  53  is attracted to and held on the outer circumferential surface of the sleeve  531  of the developing roller  53  due to the magnetic forces generated by the magnetic poles of the magnet roller  532 . In so doing, the developer  15  is held in a state in which the napped magnetic brush is formed on the outer circumferential surface of the sleeve  531  rotated in the arrow C direction. Furthermore, passing of the held developer  15  is partially regulated so as to cause the held developer  15  to have a substantially uniform layer thickness (height of the magnetic brush) when the held developer  15  passes through a required gap (regulating gap) formed between the outer circumferential surface of the sleeve  531  and the layer thickness regulating member  54  during transportation of the held developer  15  by the rotation of the sleeve  531 . 
     Next, the developer  15  having passed the layer thickness regulating member  54  is transported to the developing performing region DE facing the photoconductor drum  21  after having passed the developing opening  52  by the rotation of the sleeve  531 . The developer  15  passes through the developing performing region DE with a distal end of the magnetic brush brought into contact with the outer circumferential surface of the photoconductor drum  21 . During this passing, due to the developing (alternating) electric field formed between the developing roller  53  and the photoconductor drum  21  by the developing voltage including an alternating current supplied to the sleeve  531 , only the toner of the developer  15  is electrostatically attracted to part on the photoconductor drum  21  where the electrostatic latent image is formed while being moved in a reciprocating manner between the developing roller  53  and the photoconductor drum  21 . In this way, the developing device  5  develops the electrostatic latent image. 
     The developer  15  on the developing roller  53  that has passed through the developing performing region DE without contributing to the above-described developing step passes the developing opening  52  and is transported to the inside of the housing  50  while being held on the outer circumferential surface of the sleeve  531  due to the magnetic forces. After that, this developer  15  is principally subjected to an action of a repulsive magnetic pole of the magnet roller  532  so as to be removed from the sleeve  531  and returned to the inside of the container portion  51  (actually, the first transport path  51   a ). The removed and returned developer  15  is agitated and transported again by the agitating transport member  55  in the first transport path  51   a , and then transported in a circulating manner by passing through the second transport path  51   b  and being returned again to the first transport path  51   a  so as to be reused. 
     In addition, in the developing device  5 , the toner of the developer  15  in the container portion  51  is consumed and reduced in amount because of the supplying of the toner from the developing roller  53  to the photoconductor drum  21  due to the above-described developing operation. Accordingly, to compensate for the reduced amount of toner, the container portion  51  (the second transport path  51   b ) is replenished with new toner from a detachable toner container  18  by using a replenishing device (not illustrated) through a replenishing path (not illustrated). 
     Detailed Structure of the Developing Device 
     Meanwhile, in this developing device  5 , when the developing roller  53  (sleeve  531 ) is rotated in the arrow C direction, as exemplified by, for example, a solid arrow in  FIG. 8A , an airflow E that flows so as to move in the substantially same direction as a rotating direction C of the developing roller  53  (sleeve  531 ) is generated near the surface of the developing roller  53  (sleeve  531 ). 
     At this time, due to the rotation of the developing roller  53 , part of the airflow E passes through a gap between the developing roller  53  and a downstream edge portion  52   b  of the developing opening  52  of the housing  50  and flows to the inside of the housing  50  (container portion  51 ). 
     However, since the developing roller  53  and the agitating transport members  55 ,  56  are rotated in the housing  50  of the developing device  5  during operation, the pressure inside the housing  50  (inner pressure) is higher than the pressure outside the housing  50 . Thus, part of the airflow E (hereafter, this part of the airflow E is referred to as “airflow E 1 ”) is, as exemplified by a solid arrow in  FIG. 8B , unable to flow to the inside of the housing  50  due to obstruction caused by the pressure difference and flows in a redirected path so as to be turned around. 
     As a result, in many cases with the developing device  5 , part of the developer  15  (toner) flies up due to the effect of the airflow E 1  flowing so as to be turned around, and the flying-up developer (a so-called toner cloud) is borne by the airflow E 1  and flies so as to be dispersed to the outside of the housing  50 . 
     Here, examples of the part of the developer flying up due to the effect of the airflow E 1  include, for example, the following: part of the developer  15  that has been held at a portion of the sleeve  531  of the developing roller  53  immediately before entering the inside of the housing  50  (toner attracted to the carrier of the magnetic brush according to the present example) and is removed and flies; and the developer  15  (toner according to the present example) that is not returned to the inside of the housing  50  (container portion  51 ) and remains attracted to the downstream edge portion  52   b  of the developing opening  52  or the like. 
     Examples of spaces outside the housing  50  to which the developer  15  is scattered include, for example, the following: a gap between the developing device  5  and the photoconductor drum  21  that the developing device  5  faces; a gap between the developing device  5  and the light exposure device  23 ; and a gap from the developing device  5  to the transfer device  25  along the photoconductor drum  21 . 
     Accordingly, in the developing device  5 , a through portion  6  and a directing member  7  are provided at specified positions in the housing  50  as illustrated in, for example,  FIGS. 2 to 4 . The airflow E 1  that is part of the airflow generated by the rotation of the developing roller  53  and that does not flow to the inside of the housing  50  is introduced into and flows through the through portion  6 . The through portion  6  has an inlet  61 , an outlet  62 , and a passage  63 . The directing member  7  serving as an example of a directing device directs the airflow E 1  to the inlet  61  of the through portion  6 . 
     Out of these, the through portion  6  is provided in, as illustrated in, for example,  FIG. 3 , a portion  50   b  including the downstream edge portion  52   b  at a downstream portion of the developing opening  52  of the housing  50  in the rotating direction C of the developing roller  53 . 
     The portion  50   b  including the downstream edge portion  52   b  of the developing opening  52  projects in the direction separating from the developing roller  53  with reference to the downstream edge portion  52   b . Reference numeral  52   a  in, for example,  FIG. 3  denotes an upstream edge portion on the upstream side of the developing opening  52  in the rotating direction C of the developing roller  53 . 
     The through portion  6  allows the airflow E 1  being part of the airflow E generated by the rotation of the developing roller  53  to be introduced thereinto and flow along the outer circumferential surface of the housing  50 . Thus, the through portion  6  is a penetrated portion having a shape substantially following an outer surface of a lower portion of the housing  50 . 
     In the image forming apparatus  1  according to the first exemplary embodiment, as illustrated in  FIGS. 2 and 3 , the developing device  5  having the through portion  6  is disposed close to a position above the supply transport path Rt 1  (upstream of the supply transport path Rt 1  in the direction of gravity) upstream of the transfer position TP of the image making device  2  in the sheet  9  transport direction. That is, in the image forming apparatus  1 , a space between the developing device  5  and the supply transport path Rt 1  is comparatively small. 
     Accordingly, from the viewpoint of sufficiently allocating a transport space or the like for the sheet  9  in the supply transport path Rt 1 , it is difficult to provide the through portion  6  such that the through portion  6  passes through a lowest portion  50   fs  and extends in the direction separating from the developing opening  52 . Here, the lowest portion  50   fs  (portion closest to the supply transport path Rt 1 ) is a portion of an outer surface  50   f  of the housing  50  of the developing device  5 . The outer surface  50   f  obliquely extends downward from the downstream edge portion  52   b  of the developing opening  52  so as to approach the supply transport path Rt 1 . 
     For this reason, the through portion  6  ends at a position slightly above the lowest portion of the outer surface  50   f  of the housing  50 . In other words, the through portion  6  does not project from the lowest portion of the outer surface  50   f  toward the supply transport path Rt 1 . 
     The inlet  61  included in the through portion  6  is provided close to the downstream edge portion  52   b  of the developing opening  52  and extends in an axial direction D of the developing roller  53  in the housing  50 . As illustrated in, for example,  FIG. 5 , the inlet  61  has a plurality of (seven according to the present example) openings  61 A 1 ,  61 A 2 ,  61 A 3 ,  61 B 1 ,  61 B 1 ,  61 B 2 ,  61 B 2  separated in the axial direction D of the developing roller  53 . Each of the openings has a rectangular shape. 
     The outlet  62  included in the through portion  6  is provided below the downstream edge portion  52   b  of the developing opening  52  separated from the downstream edge portion  52   b  of the developing opening  52  by a required distance along the outer surface  50   f  below the downstream edge portion  52   b  of the developing opening  52  and extends in the axial direction D of the developing roller  53  in the housing  50 . The outlet  62  has a rectangular shape elongated in the axial direction D of the developing roller  53 . 
     Furthermore, the passage  63  included in the through portion  6  is a through space that extends along the outer surface  50   f  so as to connects the inlet  61  to the outlet  62 . The top surface (upper surface) of the passage  63  has a shape following the shape of the outer surface  50   f  of the housing  50 , and the bottom surface (lower surface) of the passage  63  is substantially flat. Furthermore, the sectional shape of the passage  63  taken along a plane along the axial direction D of the developing roller  53  has an elongated rectangular shape. 
     Furthermore, as illustrated in  FIG. 4 , the inlet  61 , the outlet  62 , and the passage  63  of the through portion  6  extend in the axial direction D of the developing roller  53  at least within the width of (the downstream edge portion  52   b  of) the developing opening  52  in the housing  50 . As illustrated in  FIG. 4 , the axial direction D of the developing roller  53  extends along a line connecting the centers of rotation of the shaft portions  531   a ,  531   b  corresponding to the rotation shaft of the developing roller  53 . 
     In the through portion  6  of the developing device  5 , as illustrated in  FIGS. 4 and 5 , an opening area S 1  of portions of the inlet  61  disposed in a central region  601  in the axial direction D of the developing roller  53  is larger than an opening area S 2  of portions of the inlet  61  disposed in both end regions  602 ,  603  in the axial direction D. That is, the inlet  61  of the through portion  6  is formed such that a magnitude relationship in which the opening area S 1 &gt; the opening area S 2  is established. 
     Here, as illustrated in  FIG. 5 , both the end regions  602 ,  603  in the axial direction D of the developing roller  53  are respectively disposed near the left and right ends in the width direction of the downstream edge portion  52   b  of the developing opening  52  and each have a width of, for example, ⅓ to ¼ of the entire width of the downstream edge portion  52   b . Meanwhile, as illustrated in  FIG. 5 , the central region  601  is disposed at a region other than both the end regions  602 ,  603 , that is, at or near the center in the width direction of the downstream edge portion  52   b  of the developing opening  52  and has a width of, for example, ½ to ⅓ of the entire width of the downstream edge portion  52   b.    
     Furthermore, the opening area S 1  of the portions disposed in the central region  601  is the total of opening areas of inlet portions disposed in the central region  601 . In the case of the inlet  61  of the present example, since three identical openings  61 A 1 ,  61 A 2 ,  61 A 3  are disposed in the central region  601 , the opening area S 1  is the total of opening areas of these openings Sa 2 , Sa 2 , Sa 2 , that is, Sa 2 +Sa 2 +Sa 2 . 
     Meanwhile, the opening area S 2  of the portions disposed in both the end regions  602 , 603  is the total of opening areas of inlet portions disposed in both the end regions  602 ,  603 . In the case of the inlet  61  of the present example, since two identical openings  61 B 1 ,  6132  are similarly disposed in each of the end region  602 , 603 , the opening area S 2  is the total of these opening areas Sb 1 , Sb 2 , Sb 1 , Sb 2 , that is, Sb 1 +Sb 2 +Sb 1 +Sb 2 . 
     Furthermore, the inlet  61  of the through portion  6  is structured such that, regarding the two identical openings  61 B 1 ,  61 B 2  disposed in each of the end regions  602 ,  603 , the magnitude relationship between the opening areas Sb 1 , Sb 2  of the openings  61 B 1 ,  61 B 2  is Sb 1 &lt;Sb 2 . Meanwhile, the inlet  61  is structured such that, regarding the three openings  61 A 1 ,  61 A 2 ,  61 A 3  disposed in the central region  601 , the magnitude relationship between the opening areas Sa 2 , Sa 2 , Sa 2  of the openings  61 A 1 ,  61 A 2 ,  61 A 3  is Sa 2 =Sa 2 =Sa 2 . 
     The seven openings  61 A 1 ,  61 A 2 ,  61 A 3 ,  61 B 1 ,  61 B 1 ,  61 B 2 ,  61 B 2  of the inlet  61  according to the first exemplary embodiment each have a width w in the direction along the axial direction D of the developing roller  53  and a height h in the direction substantially perpendicular to the axial direction D of the developing roller  53 . The seven openings  61 A 1 ,  61 A 2 ,  61 A 3 ,  61 B 1 ,  61 B 1 ,  61 B 2 ,  61 B 2  have the same width w and the height of one of three different dimensions. 
     More specifically, the height h (h 1 ) of the opening  61 B 1  disposed close to the outside in each of the end regions  602 ,  603  has a smallest dimension, the height h (h 3 ) of each of the three openings  61 A 1 ,  61 A 2 ,  61 A 3  disposed in the central region  601  has a largest dimension, and the height h (h 2 ) of the opening  61 B 2  disposed further to the inside than the opening  61 B 1  in each of the end regions  602 ,  603  is set to be an intermediate dimension (h 1 &lt;h 2 &lt;h 3 ). 
     From the viewpoint of, for example, reliably introducing the above-described airflow E 1  through the inlet  61  of the through portion  6 , the height h of each of the plurality of openings of the inlet  61  is set to be larger than the dimension of a gap L 1  ( FIG. 6 ) between the developing roller  53  and the directing member  7 , which will be described later. 
     Furthermore, the center of the height h of the seven openings  61 A 1 ,  61 A 2 ,  61 A 3 ,  61 B 1 ,  61 B 1 ,  61 B 2 ,  61 B 2  of the inlet  61  according to the first exemplary embodiment is positioned on a line extending in the axial direction D of the developing roller  53  (center line in the height direction). Also, the seven openings  61 A 1 ,  61 A 2 ,  61 A 3 ,  61 B 1 ,  61 B 1 ,  61 B 2 ,  61 B 2  are arranged in a single transverse row and spaced from one another by very small gaps of the same value (for example, about 8 to 20 mm) therebetween. 
     Meanwhile, as illustrated in, for example,  FIGS. 3 and 6 , the directing member  7  extends from a portion  50   d , which is disposed opposite to the developing opening  52  with the inlet  61  of the through portion  6  interposed therebetween in the housing  50 , toward the developing roller  53 . 
     In this case, the portion  50   d  disposed opposite to the developing opening  52  with the inlet  61  of the housing  50  interposed therebetween is formed by a substantially smooth surface that extends in the axial direction D of the developing roller  53  from an end portion  61   b  of the inlet  61  far from the downstream edge portion  52   b  of the developing opening  52  and extends toward the opposite side from the end portion  61   b . The portion  50   d  of the housing  50  according to the first exemplary embodiment is formed by a surface has an angle adjusted to a mounting angle of the substantially flat-shaped directing member  7 . 
     The directing member  7  according to the first exemplary embodiment includes a flat plate-shaped film member  70 , which is made by forming a synthetic resin film (sheet) such as polyethylene terephthalate (PET) into an elongated rectangular shape. The directing member  7  including the film member  70  is structured such that a portion including an end portion  7   a  being a free end of the film member  70  hardly shakes even when being brought into contact with an airflow generated by the rotation of the developing roller  53  or the like. Furthermore, in the case of the directing member  7  including the film member  70 , for example, a portion near an end portion  7   b  (proximal end portion) of the directing member  7  far from the developing roller  53  is mounted on and secured to the portion  50   d  of the housing  50  with a securing material such as an adhesive. 
     Furthermore, as illustrated in  FIG. 6 , the end portion (free end)  7   a  of the directing member  7  close to the developing roller  53  is not brought into contact with the developer  15  (magnetic brush) held on the surface of the developing roller  53  (sleeve  531 ). Reference numeral  15   a  in  FIG. 6  denotes a surface layer (outermost) portion of the napped magnetic brush formed by the developer  15  on the surface of the developing roller  53 . 
     Other than the above description, the inlet  61  of the through portion  6  according to the first exemplary embodiment is, as illustrated in  FIG. 7A , provided such that the openings (opening surface) of of the inlet  61  intersect a subset of tangents (such as TL 1 , TL 2 , and so forth) out of an infinite number of the tangents TL that extend in the rotating direction C of the developing roller  53  (sleeve  531 ) at the surface of the developing roller  53  (sleeve  531 ). Use of such a structure may facilitate introduction of the airflow E generated by the rotation of the developing roller  53  into the inlet  61  of the through portion  6 . Thus, dispersion of the flying developer  15  to the outside of the housing  50  may be easily suppressed. 
     The tangent TL 1  exemplified in  FIG. 7A  passes through a point of contact P 1  at the developing roller  53  (sleeve  531 ) and intersects and passes through a position near an end portion  61   a  of the inlet  61  close to the downstream edge portion  52   b  of the developing opening  52 . The tangent TL 2  exemplified in  FIG. 7A  passes through a point of contact P 2  at the developing roller  53  (sleeve  531 ) and intersects and passes through a position near the end portion  61   b  of the inlet  61  far from the downstream edge portion  52   b  of the developing opening  52 . In particular, the tangent TL 2  exemplified in  FIG. 7A  is in contact relationship with the end portion  7   a  of the directing member  7  close to the developing roller  53 . 
     Accordingly, the inlet  61  intersects at least many tangents TL existing between the two tangents TL 1  and TL 2  and also intersects a plurality of tangents existing outside the two tangents TL 1  and TL 2 . 
     Furthermore, the inlet  61  is provided such that, as illustrated in  FIG. 7B , a subset (such as PL 1  and PL 2 ) of many perpendicular lines PL to a virtual plane VP that covers the openings of the inlet  61  extend so as to pass through the surface portion DE serving as the developing performing region of the developing roller  53  (sleeve  531 ) or a region further to the inside of the developing roller  53  (the sleeve  531  and the magnet roller  532 ) than the surface portion DE. 
     With such a structure, another part of the airflow E (referred to as “airflow E 3 ” hereafter) may easily directly enter the inlet  61  of the through portion  6 , and an airflow directed by the directing member  7  may easily enter the inlet  61  as will be described later. 
     The perpendicular line PL 1  exemplified in  FIG. 7B  is an example of perpendicular lines that extend so as to pass through the surface portion DE serving as the developing performing region of the developing roller  53  (sleeve  531 ). In particular, the perpendicular line PL 1  exemplified in  FIG. 7B  is also in such a relationship with the end portion  7   a  of the directing member  7  close to the developing roller  53  that the perpendicular line PL 1  extends so as to be in contact with the end portion  7   a.    
     Furthermore, the perpendicular line PL 2  exemplified in  FIG. 7B  is an example of perpendicular lines that extend so as to pass through a region further to the inside of the developing roller  53  than the surface portion DE serving as the developing performing region of the developing roller  53  (sleeve  531 ). This perpendicular line PL 2  is also a perpendicular line extending from a position near the end portion  61   a  of the inlet  61  (plane VP) close to the downstream edge portion  52   b  of the developing opening  52 . 
     Thus, the following relationship is particularly established regarding the inlet  61 : the perpendicular lines that extend so as to pass through the region further to the inside of the developing roller  53  than the surface portion DE serving as the developing performing region of the developing roller  53  (PL 2 ) is more than the perpendicular lines that extend so as to pass through the surface portion DE serving as the developing performing region (PL 1 ). Thus, a larger part of the inlet  61  faces the developing roller  53  instead of the photoconductor drum  21 . 
     Meanwhile, as illustrated in  FIG. 6 , the end portion  7   a  of the directing member  7  according to the first exemplary embodiment close to the developing roller  53  is closer to the photoconductor drum  21  serving as an example of an image holding body that holds an electrostatic latent image to be developed than to the developing roller  53 . 
     That is, the directing member  7  at this time satisfies a magnitude relationship in which the gap L 1  that is a smallest gap between the end portion (free end)  7   a  of the directing member  7  and the developing roller  53  is larger than a smallest separation distance L 2  between the end portion  7   a  of the directing member  7  and the photoconductor drum  21  (L 1 &gt;L 2 ). 
     Furthermore, as illustrated in  FIG. 6 , the end portion  7   a  of the directing member  7  according to the first exemplary embodiment close to the developing roller  53  is closer to the developing roller  53  than a jaw portion  50   e  of the housing  50  having a shape following the circumferential surface of the developing roller  53  (sleeve  531 ). 
     That is, the directing member  7  at this time satisfies a magnitude relationship in which the gap L 1  that is a smallest gap between the end portion (free end)  7   a  of the directing member  7  and the developing roller  53  is smaller than a separation distance L 3  that is a smallest distance between the jaw portion  50   e  of the housing  50  and the developing roller  53  (L 1 &lt;L 3 ). 
     The jaw portion  50   e  of the housing  50  has an arcuate sectional shape substantially following the (radius of curvature) of the cylindrical circumferential surface of the cylindrical sleeve  531  and extends in the axial direction D of the sleeve  531  to have a belt shape. 
     Furthermore, as illustrated in  FIG. 6 , in the magnet roller  532  of the developing roller  53  of this developing device  5 , the magnetic pole N 1  at a next magnetic pole position to that of the developing magnetic pole S 1  in the rotating direction C of the sleeve  531  is disposed at a position that is deviated from the jaw portion  50   e  of the housing  50  having a shape following the circumferential surface of the cylindrical sleeve  531  and downstream of the jaw portion  50   e  in the rotating direction C of the sleeve  531 . 
     According to the first exemplary embodiment, the magnetic pole N 1  at the next magnetic pole position is used as the removing magnetic pole. Furthermore, in the magnet roller  532 , the removing magnetic pole N 1  is disposed downstream of and separated by a predetermined distance from a position in the rotating direction C of the sleeve  531 . This position faces a downstream end portion of the jaw portion  50   e  of the housing  50  in the rotating direction C. At this time, it is sufficient that the removing magnetic pole N 1  be disposed such that the peak position of a magnetic line pattern generated by the removing magnetic pole N 1  in the direction of the normal passes through the jaw portion  50   e  of the housing  50  and exists in the container portion  51  (first transport path  51   a ). 
     With such a structure, the developer  15  held on the developing roller  53  is subjected to a magnetic action caused by the removing magnetic pole N 1  of the magnet roller  532  at a portion (container portion  51 ) further to the inside than the jaw portion  50   e  of the housing  50 . Thus, the developer  15  is removed and flies up. This may reduce the likelihood of the flying developer  15  (toner) being borne by the airflow E 1 , which is generated at a portion upstream of the jaw portion  50   e  in the rotating direction C of the sleeve  531  and flowing in a folding path, so as to be transported to the outside of the housing  50 . 
     Detailed Operation of the Developing Device 
     In this developing device  5 , when predetermined time of operation of the developing device  5  comes, as described above, the airflow E, which flows so as to move in the substantially same direction as the rotating direction C of the developing roller  53 , is generated near the surface of the developing roller  53  (sleeve  531 ) being rotated ( FIG. 8A ). 
     In so doing, as indicated by a dotted arrow in  FIG. 8A , an airflow E 2  being part of the airflow E may flow into the inlet  61  of the through portion  6  that is opened near the downstream edge portion  52   b  of the developing opening  52  of the housing  50 . 
     When there is an airflow that directly flows into the inlet  61  of the through portion  6  such as the airflow E 2 , the flying toner generated due to the effect of the airflow E 1 , which will be described later and flows so as to fold back instead of flowing to the inside of the housing  50 , is borne by the airflow E 2  so as to be transported into the inlet  61  of the through portion  6 . 
     However, as has been described, the airflow E (airflow E 1 ) mostly flows in a direction so as to fold back instead of flowing to the inside of the housing  50  ( FIG. 8B ). There is a possibility that the flying developer  15  (actually, the toner) is borne by the airflow E 1  flowing so as to fold back and discharged to the outside of the housing  50 . 
     In order to address this, in the developing device  5 , the directing member  7  is provided in addition to the through portion  6 . Thus, as exemplified in  FIG. 8B , the airflow E 1  flowing so as to fold back instead of flowing to the inside of the housing  50  is brought into contact with the directing member  7  and directed so as to be introduced into the inlet  61  of the through portion  6 . That is, in the developing device  5 , the airflow E 1  flowing so as to fold back becomes the airflow E 3  introduced into the inlet  61  of the through portion  6  by being directed by the directing member  7 . 
     At this time, the above-described airflow E 2  that moves so as to directly enter the inlet  61  also exists in a region surrounded by the directing member  7 , the developing roller  53 , and the inlet  61  of the through portion  6 . This suppresses flowing of the airflow E 1  into a gap between the developing device  5  and the photoconductor drum  21  serving as an example of an outside of the housing  50  through a gap between the directing member  7  and the developing roller  53 . 
     Specifically, a portion including the end portion  7   a  at the free end the directing member  7  does not shake even when the airflow E generated by the rotation of the developing roller  53  or the airflow E 1  flowing so as to fold back is brought into contact with the directing member  7 . 
     Thus, with the developing device  5 , even when part of the developer  15  flies due to the airflow E 1  flowing so as to fold back instead of flowing to the inside of the housing  50 , dispersion of the flying developer  15  (actually, the toner) borne by the airflow E 1  so as to be discharged to the outside of the housing  50  (such as a transfer section or the gap between the developing device  5  and the photoconductor drum  21 ) may be suppressed. 
     Furthermore, the airflow E 3  introduced through the inlet  61  of the through portion  6  by being directed by the directing member  7  passes through the passage  63  and is discharged through the outlet  62  of the through portion  6  as exemplified in  FIG. 8B . 
     In so doing, the toner of the developer  15  included in the airflow E 3  is also mostly borne by the airflow E 3  so as to be discharged through the outlet  62  of the through portion  6  while partly being attracted to and remaining in the passage  63 . 
     In so doing, also, a very small amount of the toner having been discharged through the outlet  62  of the through portion  6  is discharged to the outside of the housing  50  of the developing device  5  (so as to temporarily move along the outer surface  50   f ) and drops downward. 
     In so doing, also, when the sheet  9  is transported through the supply transport path Rt 1  disposed below the developing device  5 , part of the toner discharged through the outlet  62  of the through portion  6  drops on and is attracted to a front side  9   a  of the sheet  9 . 
     This generates a fog on the front side  9   a  of the sheet  9  with such a small amount of the toner that is difficult to be recognized by the naked eye. The toner discharged through the outlet  62  of the through portion  6  at this time is collected by the sheet  9  so as to be naturally transported to the outside of the housing  10  of the image forming apparatus  1  at last, not remaining in the housing  10 . 
     In contrast, at the time when the sheet  9  is not transported through the supply transport path Rt 1 , the toner discharged through the outlet  62  of the through portion  6  is temporarily attracted to the transport guide member  13  ( FIG. 2 ) on the supply transport path Rt 1 . 
     In this developing device  5 , the airflow E 1  that does not flow to the inside of the housing  50  out of the airflow E generated by the rotation of the developing roller  53  is introduced into the inlet  61  of the through portion  6 . In so doing, as illustrated in  FIG. 9 , the airflow E 1  is introduced such that (the amount of) the airflow E 1  flowing through the openings  61 A 1 ,  61 A 2 ,  61 A 3  of the inlet  61 , which are disposed in the central region  601  in the axial direction D of the developing roller  53  and the opening area S 1  of which is relatively large, is larger than that flowing through the openings  61 B 1 ,  61 B 2  of the inlet  61 , which are disposed in both the end regions  602 ,  603  in the axial direction D of the developing roller  53  and the opening area S 2  of which is relatively small. 
     That is, as exemplified by two-dot chain line arrows E 1   a , E 1   b  in  FIG. 9 , the airflow E 1  flows while moving from both the end regions  602 ,  603  at which the openings  61 B 1 ,  61 B 2  of the inlet  61  having a relatively small opening area S 2 , and accordingly, having a small passing sectional area are disposed toward the central region  601  at which the openings  61 A 1 ,  61 A 2 ,  61 A 3  of the inlet  61  having a relatively large opening area S 1  and accordingly, having a large passing sectional area are disposed. 
     As a result, the amount of an airflow E 3   a  flowing through the openings  61 A 1 ,  61 A 2 ,  61 A 3  of the inlet  61  of the through portion  6  disposed in the central region  601  is larger than the amount of airflows E 3   c , E 3   b  flowing through the openings  61 B 1 ,  61 B 2  of the inlet  61  of the through portion  6  disposed in both the end regions  602 ,  603 . Specifically, the amount of the airflows E 3   b  flowing through the openings  61 B 2  disposed in both the end regions  602 ,  603  is larger than the amount of the airflows E 3   c  flowing through the openings  61 B 1  disposed in both the end regions  602 ,  603 . 
     Accordingly, with the developing device  5 , when the airflows (E 2 , E 3 ) are introduced through the inlet  61  of the through portion  6 , passing or remaining and existing of a relatively large amount (compared to that in the central region  601 ) of the developer  15  (toner) through or in both the end regions  602 ,  603  in the passage  63  of the through portion  6  may be suppressed. 
     Furthermore, in the image forming apparatus  1  including this developing device  5 , as schematically illustrated in  FIG. 9 , the amount of the toner passing through the passage  63  of the through portion  6  of the developing device  5  and discharged through the outlet  62  of the through portion  6  of the developing device  5  may be larger in the central region  601  than in both the end regions  602 ,  603 . 
     Thus, for example, even when images are continuously formed on sheets  9 A having a relatively small sheet width for the transportation, a relatively large amount of the toner introduced through the inlet  61  of the through portion  6  of the developing device  5  by being borne by the airflow E 1  passes through the central region  601  of the passage  63  of the through portion  6  and is discharged through the outlet  62 . The toner having been discharged drops on the sheets  9 A having a relatively small sheet width and is collected. Furthermore, remaining and existing, in both the end regions  602 ,  603  of the passage  63 , of the toner introduced into the through portion  6  at this time may be suppressed. 
     Furthermore, even when an image is formed on a sheet  9 B having a relatively large sheet width after images have been continuously formed on the sheets  9 A having a relatively small sheet width, the toner introduced into the through portion  6  of the developing device  5  is discharged through the outlet  62  of the through portion  6 , and then, much of this discharged toner may drop on a region at or near the center of the sheet  9 B having a relatively large sheet width. Thus, the toner may be more reliably collected. 
     In this case, the toner remaining in both the end regions  602 ,  603  of the passage  63  of the through portion  6  when the images have been continuously formed on the sheets  9 A having a relatively small sheet width does not necessarily drop so as to be attracted to both end portions (portions projecting in the width direction compared to the width of the sheets  9 A) of the sheet  9 B having a relatively large width. Thus, both the end portions of the sheet  9 B are not necessarily smeared with the toner. 
     Second Exemplary Embodiment 
       FIGS. 10A and 10B  illustrate a developing device according to a second exemplary embodiment. 
     A developing device  5 B according to the second exemplary embodiment has the same structure as that of the developing device  5  according to the first exemplary embodiment other than a change in through portion, that is, a through portion  6 B is used for the developing device  5 B. The through portion  6 B has a bottom surface portion  64  that is bent toward (the outer surface  50   f  of) the housing  50  between the inlet  61  and the outlet  62  of the passage  63 . 
     As illustrated in  FIG. 10A , the through portion  6 B has a bottom surface of the inner wall surface of the passage  63  facing the outer surface  50   f  of the housing  50 . As part of this bottom surface, the through portion  6 B has the bottom surface portion  64  bent toward the outer surface  50   f  of the housing  50  at a midway between the inlet  61  and the outlet  62 . 
     The bottom surface portion  64  is bent midway so as to be flexed, for example, at an angle within a range of an obtuse angle relative to part of the bottom surface extending directly from the inlet  61  under the precondition that the dimension of the outlet  62  in the vertical direction is ensured. The bottom surface portion  64  that is bent midway may be bent so as to be curved. 
     As illustrated in  FIG. 10B , in this developing device  5 B, at least part of the airflow E 3  introduced through the inlet  61  of the through portion  6 B and flowing is brought into contact with the bottom surface portion  64  bent midway when passing through the passage  63 , and then discharged through the outlet  62 . 
     Thus, the toner of the developer  15  included in the airflow E 3  is likely to be attracted to and remain in the bottom surface portion  64  of the passage  63  of the through portion  6 B. 
     Accordingly, compared to the case where the through portion does not have the bottom surface portion  64  bent midway, this developing device  5 B facilitates reduction of the amount of discharge, through the outlet  62 , of the toner of the developer  15  remaining and existing at part of the passage  63  of the through portion  6 B. 
     The toner discharged through the outlet  62  of the through portion  6 B of the developing device  5 B drops on and is attracted to the front side  9   a  of the sheet  9  passing through the supply transport path Rt 1  at the time of, for example, the image formation. In the image forming apparatus  1  including this developing device  5 B, the amount of the toner attracted to the front side  9   a  of the sheet  9  at this time is reduced compared to the case where the developing device having the through portion without the bottom surface portion  64  bent midway is provided. 
     As indicated by a two-dot chain line in  FIGS. 10A and 10B , the developing device  5 B may include a mesh member  65  at the outlet  62  of the through portion  6 B. 
     The mesh member  65  has holes (vents) having such a size that allow the air of the airflow E 3  and the toner that is included in the airflow E 3  and not flocculated to pass the holes. The mesh member  65  is provided so as to close the outlet  62 . As the mesh member  65 , for example, a member such as a nonwoven fabric is used. 
     With the developing device  5 B having the through portion  6 B provided with the above-described mesh member  65 , the toner of the developer  15  remaining and existing in the passage  63  of the through portion  6 B is discharged while being adjusted to be averaged by passing through the mesh member  65  when discharged through the outlet  62 . 
     For example, when the developing device  5 B alone or the developing device  5 B together with another element (device) of the image making device  2  is detachable from the housing  10  of the image forming apparatus  1 , the developing device  5 B may be subjected to external shocks due to contact or the vibration of the developing device  5 B during detachment/attachment. However, even in such a case, the above-described structure with the mesh member  65  may reduce the likelihood of the toner of the developer  15  that remains and exists in the passage  63  of the through portion  6 B of the developing device  5 B being discharged and dropping (such as dripping) through the outlet  62  in a state in which the toner is flocculated into blocks. 
     This mesh member  65  is also able to be provided at the outlet  62  of the through portion  6  of the developing device  5  according to the first exemplary embodiment. 
     Also with the developing device  5  provided with the mesh member  65  as described above, operating features similar to the case with the developing device  5 B may be obtained. 
     Third Exemplary Embodiment 
       FIGS. 11 to 13  illustrate a developing device according to a third exemplary embodiment. 
     A developing device  5 C according to the third exemplary embodiment is changed from the developing device  5  according to the first exemplary embodiment as follows. That is, as the through portion, a through portion  6 C is used. The inlet  61  of the through portion  6 C has a plurality of openings having the same opening area. In addition, side openings  67  provided in side surfaces, respectively, at both ends of the passage  63  and air supply devices  68  that supply air from the respective side openings  67  toward the center of the passage  63  are provided for the through portion  6 C. Other than these, the developing device  5 C according to the third exemplary embodiment has the same structure as that of the developing device  5  according to the first exemplary embodiment. 
     As illustrated in  FIG. 13 , the through portion  6 C of the developing device  5 C has the inlet  61  having seven openings  61 X of the same rectangular opening shape. Thus, an opening area Sax of each of the openings  61 X of portions disposed in the central region  601  in the axial direction D of the inlet  61  and an opening area Sbx of each of the openings  61 X disposed in both the end regions  602 ,  603  in the axial direction D of the inlet  61  are the same. 
     Accordingly, in the through portion  6 C, the size (area) of the opening area S 1  of portions of the inlet  61  disposed in the central region  601  in the axial direction D is the same as the size (area) of the opening area S 2  of portions of the inlet  61  disposed in both the end regions  602 ,  603  in the axial direction D. 
     Furthermore, as illustrated in  FIGS. 11 to 13 , this through portion  6 C has side openings  67 A,  67 B in the side surfaces at both the ends of the passage  63  (side wall surfaces of the housing  50 ) in the axial direction D of the developing roller  53 . Furthermore, as illustrated in  FIGS. 12 and 13 , the through portion  6 C is provided with the air supply devices  68  that respectively supply air Em flowing from the side openings  67 A,  67 B of the passage  63  toward the center of the passage  63  in the axial direction D. 
     The side openings  67 A,  67 B are through holes that are, for example, openings having a vertically long rectangular opening shape as illustrated in  FIG. 12 . 
     The side openings  67 A,  67 B according to the third exemplary embodiment are passages obliquely penetrating through the housing  50  toward the outlet  62  from the outside toward the inside of the housing  50  so as to allow, for example, as illustrated in  FIG. 13 , the air Em to be supplied therethrough such that the air Em moves in the oblique direction so as to approach the outlet  62  as the air Em moves toward the center of the passage  63  of the through portion  6 C in the axial direction D. 
     The air supply devices  68  include introduction tubes disposed so as to introduce the air as the air Em into the passage  63  of the through portion  6 C by utilizing part of an airflow naturally or artificially generated in the housing  10  of the image forming apparatus  1 . 
     The air supply devices  68  may have another structure than the above-described structure. For example, the air supply devices  68  may actively supply the air Em by using dedicated fans and blower tubes. 
     In the developing device  5 C including such a through portion  6 C, the airflow E 1  that does not flow to the inside of the housing  50  out of the airflow E generated by the rotation of the developing roller  53  is introduced into the inlet  61  of the through portion  6 C. In so doing, as illustrated in  FIG. 13 , the airflow E 1  is introduced such that the amounts of the airflow E 1  flowing through the seven openings  61 X of the inlet  61  having the same opening shape and the same area is substantially the same. 
     Meanwhile, with the through portion  6 C, as illustrated in  FIG. 13 , air Ema, Emb from the air supply devices  68  is supplied into the passage  63  through the side openings  67 A,  67 B, respectively. The air Ema, Emb at this time is, as exemplified by two-dot chain line arrows Ema, Emb in  FIG. 13 , supplied to move in the oblique direction so as to approach the outlet  62  as the air Ema, Emb moves toward the center in the axial direction D of the passage  63 . 
     As a result, the airflow E 3  introduced through the seven openings  61 X of the inlet  61  of the through portion  6 C flows through the passage  63  as follows. 
     First, as illustrated in  FIG. 13 , airflows E 3   a   4 , E 3   a   5  flowing through the two openings  61 X disposed in the end region  602  of the passage  63  and the two openings  61 X disposed in the end region  603  of the passage  63  are subjected to relatively large flowing forces (wind forces) of the air Emb, Ema supplied through the side openings  67 B,  67 A, thereby flowing so as to move in a flowing paths bent toward the central region  601  of the passage  63 . 
     Meanwhile, airflows E 3   a   1 , E 3   a   2 , E 3   a   3  flowing through the three openings  61 X disposed in the central region  601  of the passage  63  are subjected to the relatively small flowing forces (wind forces) of the air Ema, Emb, thereby flowing substantially straightly through the central region  601  of the passage  63  substantially without a change in flowing paths. Out of these, the airflows E 3   a   2 , E 3   a   3  flowing through the openings  61 X disposed close to the respective end regions  602 ,  603  in the central region  601  of the passage  63  are slightly subjected to the flowing forces (wind forces) of the air Emb, Ema, thereby flowing so as to be slightly bent toward the central region  601  of the passage  63  due to changes in flowing paths. 
     That is, as exemplified by two-dot chain line arrows E 3   a , E 3   b  in  FIG. 13 , the airflow E 1  introduced through the inlet  61  of the through portion  6 C flows, when passing through the passage  63  of the through portion  6 C, so as to be gathered (be concentrated) from the both the end regions  602 ,  603  toward the central region  601  in the passage  63  by the action of the air Emb, Ema. 
     As a result, regarding the amount the airflow during passing through the passage  63  of the through portion  6 C and discharge through the outlet  62  of the through portion  6 C, the amount of the airflow flowing through the central region  601  of the passage  63  is larger than the amount of the airflow flowing through both the end regions  602 ,  603  of the passage  63 . 
     Accordingly, also with the developing device  5 C, when the air flows (E 2 , E 3 ) are introduced through the inlet  61  of the through portion  6 C, passing or remaining and existing of a relatively large amount (compared to that in the central region  601 ) of the developer  15  (toner) through or in both the end regions  602 ,  603  in the passage  63  of the through portion  6 C may be suppressed. 
     Furthermore, in the image forming apparatus  1  including this developing device  5 C, almost similarly to the case of the image forming apparatus  1  including the developing device  5  according to the first exemplary embodiment, the amount of the toner passing through the passage  63  of the through portion  6 C of the developing device  5 C and discharged through the outlet  62  of the through portion  6 C of the developing device  5 C may be larger in the central region  601  than in both the end regions  602 ,  603 . 
     Thus, almost similarly to the case of the image forming apparatus  1  including the developing device  5  according to the first exemplary embodiment (see  FIG. 9 ), for example, even when images are continuously formed on the sheets  9 A having a relatively small sheet width for the transportation, a relatively large amount of the toner introduced through the inlet  61  of the through portion  6 C of the developing device  5 C by being borne by the air flow E 1  passes through the central region  601  of the passage  63  of the through portion  6 C and is discharged through the outlet  62 . The toner having been discharged drops on the sheets  9 A having a relatively small sheet width and is collected. Furthermore, remaining and existing, in both the end regions  602 ,  603  of the passage  63 , of the toner introduced into the through portion  6 C at this time may be suppressed. 
     Furthermore, even when an image is formed on the sheet  9 B having a relatively large sheet width after images have been continuously formed on the sheets  9 A having a relatively small sheet width, the toner introduced into the through portion  6 C of the developing device  5 C is discharged through the outlet  62  of the through portion  6 C, and then, much of this discharged toner may drop on a region at or near the center of the sheet  9 B having a relatively large sheet width. Thus, the toner may be more reliably collected. 
     In this case, the toner remaining in both the end regions  602 ,  603  of the passage  63  of the through portion  6 C when the images have been continuously formed on the sheets  9 A having a relatively small sheet width does not necessarily drop so as to be attracted to both the end portions of the sheet  9 B having a relatively large width. Thus, both the end portions of the sheet  9 B are not necessarily smeared with the toner. 
     Fourth Exemplary Embodiment 
       FIG. 14  illustrates part of a developing device according to a fourth exemplary embodiment. 
     A developing device  5 D according to the fourth exemplary embodiment is changed from the developing device  5  according to the first exemplary embodiment as follows. That is, as the through portion, a through portion  6 D is used. The through portion  6 D is provided with the side openings  67  in the side surfaces, respectively, at both the ends of the passage  63  and the air supply devices  68  that supply the air from the respective side openings  67  toward the center of the passage  63 . Other than these, the developing device  5 D according to the fourth exemplary embodiment has the same structure as that of the developing device  5  according to the first exemplary embodiment. 
     It is able to be described that the developing device  5 D has the same structure as that of the developing device  5 C according to the third exemplary embodiment other than that the developing device  5 D is changed from the developing device  5 C by using, as the through portion, a structure in which the relationships between the opening areas are similar to or the same as those of the inlet  61  according to the first exemplary embodiment. 
     The inlet  61  of the through portion  6 D has the same structure as that of the inlet  61  according to the first exemplary embodiment ( FIG. 5 ). 
     Furthermore, the side openings  67 A,  67 B and the air supply devices  68  at the through portion  6 D have the same structures as those of the side openings  67 A,  67 B and the air supply devices  68  according to the third exemplary embodiment ( FIGS. 11 to 13 ). 
     In the developing device  5 D having such a through portion  6 D, the airflow E 1  that does not flow to the inside of the housing  50  out of the airflow E generated by the rotation of the developing roller  53  is introduced into the inlet  61  of the through portion  6 D. In so doing, the airflow E 1  is introduced such that (the amount of) the airflow E 1  flowing through the openings  61 A 1 ,  61 A 2 ,  61 A 3  of the inlet  61 , which are disposed in the central region  601  in the axial direction D of the developing roller  53  and the opening area S 1  of which is relatively large, is larger than that flowing through the openings  61 B 1 ,  61 B 2  of the inlet  61 , which are disposed in both the end regions  602 ,  603  in the axial direction D of the developing roller  53  and the opening area S 2  of which is relatively small (see  FIG. 9 ). 
     Meanwhile, in the through portion  6 D at this time, as illustrated in  FIG. 14 , the air Ema, Emb from the air supply devices  68  is supplied into the passage  63  through the side openings  67 A,  67 B, respectively. The air Ema, Emb at this time is, as exemplified by two-dot chain line arrows Ema, Emb in  FIG. 14 , supplied to move in the oblique direction so as to approach the outlet  62  as the air Ema, Emb moves toward the center in the axial direction D of the passage  63 . 
     As a result, the airflow E 3  introduced through the seven openings  61 A 1 ,  61 A 2 ,  61 A 3 ,  61 B 1 ,  61 B 2 ,  61 B 1 ,  61 B 2  of the inlet  61  of the through portion  6 D flows through the passage  63  as follows. 
     First, as illustrated in  FIG. 14 , airflows E 3   c    1 , E 3   b   1  of relatively small air flow amounts and flowing through the two openings  61 B 1 ,  61 B 2  disposed in the end region  602  of the passage  63  and the two openings  61 B 1 ,  61 B 2  disposed in the end region  603  of the passage  63  are subjected to relatively large flowing forces (wind forces) of the air Emb, Ema supplied through the side openings  67 B,  67 A, thereby flowing so as to move in a flowing paths bent toward the central region  601  of the passage  63 . 
     Meanwhile, airflows E 3   a   1 , E 3   a   2 , E 3   a   3  flowing through the three openings  61 A 1 ,  61 A 2 ,  61 A 3  disposed in the central region  601  of the passage  63  are subjected to the relatively small flowing forces of the air Ema, Emb, thereby flowing substantially straightly through the central region  601  of the passage  63  substantially without a change in flowing paths. Out of these, the airflows E 3   a   2 , E 3   a   3  flowing through the openings  61 A 2 ,  61 A 3  disposed close to the respective end regions  602 ,  603  in the central region  601  of the passage  63  are slightly subjected to the flowing forces of the air Emb, Ema, thereby flowing so as to be slightly bent toward the central region  601  of the passage  63  due to changes in flowing paths. 
     That is, as exemplified by two-dot chain line arrows E 1   a , E 1   b  in  FIG. 14 , the airflow E 1  introduced through the inlet  61  of the through portion  6 D flows while moving from both the end regions  602 ,  603  at which the openings  61 B 1 ,  61 B 2  of the inlet  61  having a relatively small opening area S 2 , and accordingly, having a small passing sectional area are disposed toward the central region  601  at which the openings  61 A 1 ,  61 A 2 ,  61 A 3  of the inlet  61  having a relatively large opening area S 1 , and accordingly, having a large passing sectional area are disposed. 
     Furthermore, as exemplified by two-dot chain line arrows E 3   a , E 3   b  in  FIG. 14 , the airflow E 1  having been introduced through the inlet  61  of the through portion  6 D flows, when passing through the passage  63  of the through portion  6 D, so as to be gathered from the both the end regions  602 ,  603  toward the central region  601  in the passage  63  by the action of the air Emb, Ema. 
     As a result, the amount of an airflow E 3   a  flowing through the openings  61 A 1 ,  61 A 2 ,  61 A 3  of the inlet  61  of the through portion  6 D disposed in the central region  601  is larger than the amount of airflows E 3   c , E 3   b  flowing through the openings  61 B 1 ,  61 B 2  of the inlet  61  of the through portion  6 D disposed in both the end regions  602 ,  603 . Furthermore, regarding the amount the airflow during passing through the passage  63  of the through portion  6 D and discharge through the outlet  62  of the through portion  6 D, the amount of the airflow flowing through the central region  601  of the passage  63  is larger than the amount of the airflow flowing through both the end regions  602 ,  603  of the passage  63 . 
     Accordingly, with the developing device  5 D, when the air flows (E 2 , E 3 ) are introduced through the inlet  61  of the through portion  6 D, passing or remaining and existing of a relatively large amount (compared to that in the central region  601 ) of the developer  15  (toner) through or in both the end regions  602 ,  603  in the passage  63  of the through portion  6 D may be more reliably suppressed than with the developing devices  5 ,  5 C. 
     Furthermore, in the image forming apparatus  1  including this developing device  5 D, almost similarly to the case of the image forming apparatus  1  including the developing device  5  according to the first exemplary embodiment or the image forming apparatus  1  including the developing device  5 C according to the third exemplary embodiment, it may be more reliably ensured that the amount of the toner passing through the passage  63  of the through portion  6 D of the developing device  5 D and discharged through the outlet  62  of the through portion  6 D of the developing device  5 D is larger in the central region  601  than that in both the end regions  602 ,  603 . 
     Variations 
     For the first, second, and fourth exemplary embodiments, instead of the corresponding (inlets  61 ) of the through portions  6 ,  6 B,  6 D of the developing devices  5 ,  5 B,  5 D, for example, any of through portions  6 E,  6 F,  6 G,  6 H having respective inlets of the following varied structures may be used. 
     The through portion  6 E exemplified in  FIG. 15  has the inlet  61  having the total of 15 divided openings as follows: six openings  61 B 4 ,  61 B 5 ,  61 B 6 ,  61 B 7 ,  61 B 8 ,  61 B 9  that have the same height h and rectangular opening shapes and that is disposed in each of the end regions  602 ,  603 ; and three openings  61 A 1 ,  61 A 2 ,  61 A 3  that have a height h being the same as the height h of the six openings and the same rectangular opening shape and that is disposed in the central region  601 . 
     Out of these, widths w of the six openings  61 B 4 ,  61 B 5 ,  61 B 6 ,  61 B 7 ,  61 B 8 ,  61 B 9  disposed in each of the end regions  602 ,  603  gradually increase in this order. Opening areas Sb 4 , Sb 5 , Sb 6 , Sb 6 , Sb 7 , Sb 8 , Sb 9  of these six openings also increase in this order because the six openings have the same height h. 
     The following relationship is established in the inlet  61  of through portion  6 E: the opening area S 1  that is the total of the opening areas Sa 2 , Sa 2 , Sa 2  (Sa 2 +Sa 2 +Sa 2 ) of the three same openings  61 A 1 ,  61 A 2 ,  61 A 3  disposed in the central region  601  is larger than the opening area S 2  that is double the total of the opening areas Sb 4 , Sb 5 , Sb 6 , Sb 7 , Sb 8 , Sb 9  ((Sb 4 +Sb 5 +Sb 6 +Sb 7 +Sb 8 +Sb 9 )×2) of the six openings  61 B 4 ,  61 B 5 ,  61 B 6 ,  61 B 7 ,  61 B 8 ,  61 B 9  disposed in each of the end regions  602 ,  603 . 
     The through portion  6 F exemplified in  FIG. 16  has the inlet  61  having the total of 11 divided openings as follows: four openings  61 C 1 ,  61 C 2 ,  61 C 3 ,  61 C 4  the opening shapes of which are trapezoidal shapes turned sideways and which are disposed in each of the end regions  602 ,  603 ; and three openings  61 A 1 ,  61 A 2 ,  61 A 3  that have the same height h and the same rectangular opening shape and that is disposed in the central region  601 . 
     Out of these, widths w of the four openings  61 C 1 ,  61 C 2 ,  61 C 3 ,  61 C 4  disposed in each the end regions  602 ,  603  gradually increase in this order. Furthermore, each of the four openings  61 C 1 ,  61 C 2 ,  61 C 3 ,  61 C 4  has left and right heights h 1 , h 2  different from each other, and the heights h 2  of the openings  61 C 1 ,  61 C 2 ,  61 C 3  are respectively the same as the heights h 1  of the adjacent openings  61 C 2 ,  61 C 3 ,  61 C 4 . Thus, the left and right heights h 1 , h 2  of the openings  61 C 1 ,  61 C 2 ,  61 C 3 ,  61 C 4  gradually increase in this order. Lower sides of the four openings  61 C 1 ,  61 C 2 ,  61 C 3 ,  61 C 4  are at the same level and coincident with a line extending, in the axial direction D, through lower sides of the three same openings  61 A 1 ,  61 A 2 ,  61 A 3  disposed in the central region  601 . In contrast, upper sides of the four openings  61 C 1 ,  61 C 2 ,  61 C 3 ,  61 C 4  are inclined such that the level of the upper sides gradually increases from the left or right end toward the central region  601 . 
     The following relationship is established in the inlet  61  of the through portion  6 F: the opening area S 1  that is the total of the opening areas Sa 2 , Sa 2 , Sa 2  (Sa 2 +Sa 2 +Sa 2 ) of the three same openings  61 A 1 ,  61 A 2 ,  61 A 3  disposed in the central region  601  is larger than the opening area S 2  that is double the total of opening areas Sc 1 , Sc 2 , Sc 3 , Sc 4  ((Sc 1 +Sc 2 +Sc 3 +Sc 4 )×2) of the four openings  61 C 1 ,  61 C 2 ,  61 C 3 ,  61 C 4 , disposed in each of the end regions  602 ,  603 . 
     In particular, the opening areas Sc 1 , Sc 2 , Sc 3 , Sc 4  of the four openings  61 C 1 ,  61 C 2 ,  61 C 3 ,  61 C 4  of the inlet  61  of the through portion  6 F disposed in each of the end regions  602 ,  603  increase toward the central region  601 . Thus, the differences in amount of the toner of the developer  15  passing through or remaining and existing in both the end regions  602 ,  603  of the passage  63  of the through portion  6 F may be smoothly reduced with less stepwise reductions. 
     It is also possible to make the opening areas Sa 2 , Sa 2 , Sa 2  of the three same openings  61 A 1 ,  61 A 2 ,  61 A 3  of the inlet  61  of the through portion  6 F disposed in the central region  601  increase toward the central position of the central region  601  in the axial direction D. With the through portion  6 F having such a structure, the differences in amount of the toner of the developer  15  passing through or remaining and existing in the central region  601  of the passage  63  of the through portion  6 F in addition to both the end regions  602 ,  603  of the passage  63  may be smoothly reduced with less stepwise reductions. 
     The through portion  6 G exemplified in  FIG. 17  has the inlet  61  having the total of 9 divided openings as follows: four openings  61 D 1 ,  61 D 2 ,  61 D 3 ,  61 D 4  that have right triangular opening shapes and that are disposed in each of the end regions  602 ,  603 ; and a single opening  61 A 4  that has a rectangular opening shape and that is disposed in the central region  601 . 
     Out of these, widths w of the four openings  61 D 1 ,  61 D 2 ,  61 D 3 ,  61 D 4  disposed in each the end regions  602 ,  603  gradually increase in this order. Furthermore, heights h of the four openings  61 D 1 ,  61 D 2 ,  61 D 3 ,  61 D 4  also gradually increase in this order. Lower sides of the four openings  61 D 1 ,  61 D 2 ,  61 D 3 ,  61 D 4  are at the same level and coincident with a line extending, in the axial direction D, through a lower side of the single opening  61 A 4  disposed in the central region  601 . In contrast, hypotenuses of the four openings  61 D 1 ,  61 D 2 ,  61 D 3 ,  61 D 4  gradually increase in length from the left or right end toward the central region  601 . 
     The following relationship is established in the inlet  61  of through portion  6 G: the opening area S 1  that is an opening area Sa 4  of the single opening  61 A 4  disposed in the central region  601  is larger than the opening area S 2  that is double the total of opening areas Sd 1 , Sd 2 , Sd 3 , Sd 4  ((Sd 1 +Sd 2 +Sd 3 +Sd 4 )×2) of the four openings  61 D 1 ,  61 D 2 ,  61 D 3 ,  61 D 4  disposed in each of the end regions  602 ,  603 . 
     The through portion  6 H exemplified in  FIG. 18  has the inlet  61  having a single continual opening the opening shape (area) of which gradually increases from both the end regions  602 ,  603  toward the central region  601 . 
     That is, the inlet  61  having this single continual opening includes a single inlet central portion  61   a  that has a largest rectangular opening shape and that is disposed in the central region  601  and two inlet end portions  61   b ,  61   c  that have an elongated rectangular shape the height of which gradually reduces and that is disposed in each of the end regions  602 ,  603 . The two inlet end portions  61   b ,  61   c  has the same width w and the height that is smaller than a height h of the inlet central portion  61   a  and further reduces toward the end. Meanwhile, the single inlet central portion  61   a  has the height h and a width w that are respectively larger than a height h and the width w of the two inlet end portions  61   b ,  61   c.    
     The following relationship is established in the inlet  61  of through portion  6 H: the opening area S 1  that is an opening area S 10  of the inlet central portion  61   a  disposed in the central region  601  is larger than the opening area S 2  that is double the total of opening areas S 11 , S 12  ((S 11 +S 12 )×2) of the two inlet end portions  61   b ,  61   c  disposed in each of the end regions  602 ,  603 . 
     Furthermore, the inlet  61  having a plurality of divided openings of any of the through portions  6 ,  6 B,  6 D according to the first, second, and fourth exemplary embodiments is able to have a structure having a single continual inlet similarly to that of the through portion  6 H exemplified in  FIG. 18 . 
     Other than the above description, the inlet  61  of the through portion  6  or the like having the plurality of divided openings may have the following structures. 
     Examples of the other inlet  61  include, for example, an inlet which have openings the shape of which is other than the above-described shapes such as a circular or elliptical shape arranged in a single or a plurality of rows and in which the opening area S 1  that is the total of opening areas of all the openings disposed in the central region  601  is larger than the opening area S 2  that is the total of opening areas of all the openings disposed in both the end regions  602 ,  603 . 
     The opening area S 1  and the opening area S 2  of the inlet  61  are adjusted by changing the conditions relating to the dimensions such as heights h, widths w, lengths of sides, and states of curves of the openings of the inlet  61 . 
     As the mesh member  65  provided at the outlet  62  of the through portion  6 B according to the second exemplary embodiment, a member having holes of a uniform size (roughness) in the entirety of the member is exemplified. However, as the mesh member  65 , a mesh member in which the size of the holes (coarseness) is varied between the central region  601  and both the end regions  602 ,  603  of the outlet  62  in the axial direction D may be used. Specifically, the mesh member  65  in which the size of the holes (coarseness) in the central region  601  of the outlet  62  is larger than the size of the holes (coarseness) in both the end regions  602 ,  603  of the outlet  62  is used. 
     With the through portion  6 B (including the through portion  6  according to the first exemplary embodiment) provided with such a mesh member  65 , due to the variation in size of the holes of the mesh member  65 , when the air flow E 1  having introduced into the through portion  6 B ( 6 ) is discharged through the outlet  62 , the occurrences of a situation in which the amount of the toner of the developer  15  discharged through both the end regions  602 ,  603  of the outlet  62  exceeds that discharged through the central region  601  of the outlet  62  may be suppressed. 
     In addition, although the image forming apparatus  1  that uses a single developing device  5  ( 5 B,  5 C,  5 D) so as to form monochrome images is exemplified according to the first to fourth exemplary embodiments, the image forming apparatus according to the disclosure may use a plurality of developing devices  5  ( 5 B,  5 C,  5 D) so as to form multi-color images. 
     Furthermore, the developing device  5  ( 5 B,  5 C,  5 D) may be disposed and used above an inclined sheet transport path as a sheet transport path through which the sheet  9  is transported. 
     The foregoing description of the exemplary embodiments of the present disclosure has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure 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 disclosure and its practical applications, thereby enabling others skilled in the art to understand the disclosure for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the following claims and their equivalents.