Patent Publication Number: US-9851690-B2

Title: Image forming apparatus and movable drawer

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/015,788 filed on Feb. 4, 2016, which claims priority from Japanese Patent Application No. 2015-022593, filed on Feb. 6, 2015, which are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     Aspects described herein relate to an electrophotographic image forming apparatus and a movable member attached to the image forming apparatus. 
     BACKGROUND 
     A known electrophotographic tandem-type image forming apparatus includes a plurality of process cartridges each including a photosensitive drum for one of colors (e.g., yellow, magenta, cyan, and black). 
     The known image forming apparatus further includes a drawer frame having a generally box shape. The drawer frame is configured to accommodate the plurality of process cartridges therein. The drawer frame is movable between a position inside a main body of the image forming apparatus and a position outside the main body of the image forming apparatus for having one or more of the plurality of process cartridges attached thereto or detached therefrom. 
     SUMMARY 
     Nevertheless, in the image forming apparatus, the drawer frame has a generally box shape. Therefore, a configuration for transmitting a driving force to the photosensitive drums of the process cartridges accommodated in the drawer frame may be complicated. Further, the drawer frame may be configured to accommodate the plurality of process cartridges therein, whereby the drawer frame may have a relatively large size. 
     Accordingly, some embodiments of the disclosure provide for an image forming apparatus having a reduced size and a movable member having a reduced size and a simple configuration. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Aspects of the disclosure are illustrated by way of example and not by limitation in the accompanying figures in which like reference characters indicate similar elements. 
         FIG. 1  is a central sectional view depicting a printer as an image forming apparatus in a first illustrative embodiment according to one or more aspects of the disclosure, wherein a drawer is located at an adjacent position of an inside position. 
         FIG. 2  is a sectional view taken along line A-A of the printer of  FIG. 1  in the first illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 3  is an upper front perspective view depicting a drawer of  FIG. 1  in the first illustrative embodiment according to one or more aspects of the disclosure, wherein a frontmost support surface supports a process cartridge. 
         FIG. 4  is a sectional view taken along line B-B of the printer of  FIG. 2  in the first illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 5  is a sectional view taken along line C-C of the printer of  FIG. 2  in the first illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 6  is a sectional view taken along line D-D of the printer of  FIG. 2  in the first illustrative embodiment according to one or more aspects of the disclosure, wherein developing units are illustrated in plan view for convenience in drawing. 
         FIG. 7  is a sectional view depicting the printer of  FIG. 5  in the first illustrative embodiment according to one or more aspects of the disclosure, wherein a protrusion of a front cover and a translation cam are disengaged from each other. 
         FIG. 8  is a sectional view depicting the printer of  FIG. 6  in the first illustrative embodiment according to one or more aspects of the disclosure, wherein the protrusion of the front cover and the translation cam are disengaged from each other. 
         FIG. 9  is a sectional view depicting the printer of  FIG. 5  in the first illustrative embodiment according to one or more aspects of the disclosure, wherein the front cover is located at an exposing position and the drawer is located at a distant position of the inside position. 
         FIG. 10  is a sectional view depicting the printer of  FIG. 2  in the first illustrative embodiment according to one or more aspects of the disclosure, wherein the drawer is located at the distant position of the inside position. 
         FIG. 11  is a sectional view depicting the printer of  FIG. 1  in the first illustrative embodiment according to one or more aspects of the disclosure, wherein the drawer is located at an outside position. 
         FIG. 12  is an upper front perspective view depicting a drawer of a printer in a second illustrative embodiment according to one or more aspects of the disclosure, wherein a frontmost support surface supports a process cartridge. 
         FIG. 13  is an upper front perspective view depicting a drawer of a printer in a third illustrative embodiment according to one or more aspects of the disclosure, wherein a frontmost support surface supports a process cartridge. 
         FIG. 14  is an upper front perspective view depicting a drawer of a printer in a fourth illustrative embodiment according to one or more aspects of the disclosure, wherein a frontmost support surface supports a process cartridge. 
         FIG. 15  is a central sectional view depicting a printer in a fifth illustrative embodiment according to one or more aspects of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     For a more complete understanding of the present disclosure, needs satisfied thereby, and the objects, features, and advantages thereof, reference now is made to the following descriptions taken in connection with the accompanying drawings. Hereinafter, illustrative embodiments of the disclosure will be described in detail with reference to the accompanying drawings. 
     1. Overall Configuration of Printer 
     As depicted in  FIG. 1 , a printer  1  (as an example of an image forming apparatus) may be an intermediate transfer type color printer in which process cartridges  14  are arranged side by side in a horizontal direction. 
     With reference to the printer  1 , directions of up, down, right, left, front, and rear may be defined with reference to an orientation of the printer  1  that is disposed in which it is intended to be used as depicted in  FIG. 1 . 
     The printer  1  includes a casing  2 , an image forming unit  4 , a discharge unit  5 , and an image reading unit  6 . The image forming unit  4  forms an image onto a sheet P. The discharge unit  5  discharges a sheet P having an image formed thereon. The image reading unit  6  reads image information from a document. 
     The casing  2  has a generally box shape and has an opening  20 . The casing  2  includes a front cover  7  and a sheet feed tray  8 . 
     The opening  20  is defined in a front end portion of the casing  2 . The opening  20  provides communication between the inside and the outside of the casing  2  in a front-rear direction (as an example of a sliding direction) of the printer  1 . 
     The front cover  7  is swingable between a closing position (e.g., a position of the front cover  7  depicted in  FIG. 1 ) and an exposing position (e.g., a position of the front cover  7  depicted in  FIGS. 9 and 11 ) on its lower end portion of a front wall of the casing  2 . When the front cover  7  is located at the closing position (refer to  FIG. 1 ), the front cover  7  closes the opening  20 . When the front cover  7  is located at the exposing position (refer to  FIGS. 9 and 11 ), the front cover  7  exposes the opening  20 . 
     As depicted in  FIG. 1 , the sheet feed tray  8  is disposed in a lower end portion of the casing  2 . The sheet feed tray  8  is detachably attachable to the casing  2 . The sheet feed tray  8  is configured to support one or more sheets P thereon. The one or more sheets P supported by the sheet feed tray  8  are conveyed one by one to between an intermediate transfer belt  44  and a secondary transfer roller  41  by rotation of rollers at a predetermined timing. 
     An upper surface of the casing  2  is defined as a sheet discharge tray  54 . 
     The image forming unit  4  includes an exposing device  15 , a drawer  16 , a plurality of, for example, four, process cartridges  14 , a transfer unit  17 , and a fixing unit  18 . 
     The exposing device  15  is disposed in an upper end portion of the casing  2 . As indicated by solid lines in  FIG. 1 , the exposing device  15  emits laser beams toward a plurality of, for example, four, photosensitive drums  25 , respectively, based on image data to expose surfaces of the photosensitive drums  25 . 
     The drawer  16  is disposed below the exposing device  15  in a substantially middle portion of the casing  2  in an up-down direction. 
     The process cartridges  14  each include the photosensitive drum  25 , a charging roller  30 , and a developing unit  32 . The charging roller  30  charges the surface of the photosensitive drum  25 . The developing unit  32  develops an electrostatic latent image, which is formed on the surface of the photosensitive drum  25  by the exposing device  15 , to a toner image. The process cartridges  14  are supported by the drawer  16 . 
     The transfer unit  17  is disposed below the drawer  16  and above the sheet feed tray  8  in a lower portion of the casing  2 . The transfer unit  17  includes a belt unit  40  and the secondary transfer roller  41 . 
     The belt unit  40  extends along the front-rear direction such that the belt unit  40  is disposed below all of the photosensitive drums  25 . The belt unit  40  includes a drive roller  42 , a driven roller  43 , a tension roller  46 , the intermediate transfer belt  44  (as an example of a transfer medium), and a plurality of, for example, four, primary transfer rollers  45 . The primary transfer rollers  45  perform primary transfer for transferring toner images formed on the surfaces of the photosensitive drums  25 , respectively, onto the intermediate transfer belt  44 . 
     The drive roller  42  is rotatably disposed at a rear end portion of the belt unit  40 . 
     The driven roller  43  is rotatably disposed at a front end portion of the belt unit  40 . 
     The tension roller  46  is disposed lower and further to the front than the drive roller  42  while being rotatably disposed a lower rear portion of the belt unit  40 . 
     The intermediate transfer belt  44  is wound around the drive roller  42 , the driven roller  43 , and the tension roller  46  such that an outer surface of an upper portion of the intermediate transfer belt  44  is in contact with lower end portions of all of the photosensitive drums  25 . The intermediate transfer belt  44  rotates by rotation of the drive roller  42  and by rotation of the driven roller  43  caused following the rotation of the drive roller  42  such that the upper portion of the intermediate transfer belt  44  moves frontward. The tension roller  46  presses a lower portion of the intermediate transfer belt  44  downward to provide a tension on the intermediate transfer belt  44 . 
     The primary transfer rollers  45  are arranged side by side between the drive roller  42  and the driven roller  43  in the front-rear direction while being spaced apart from each other in the front-rear direction. The primary transfer rollers  45  are disposed below the respective photosensitive drums  25  such that the primary transfer rollers  45  are across the intermediate transfer belt  44  from the respective photosensitive drums  25 . The primary transfer rollers  45  are in contact with an inner surface of the upper portion of the intermediate transfer belt  44  from below. 
     The secondary transfer roller  41  is disposed lower and further to the rear than the drive roller  42  in the belt unit  40  while being across the intermediate transfer belt  44  from the drive roller  42 . The secondary transfer roller  41  performs secondary transfer for transferring a color image formed on the surface of the intermediate transfer belt  44  onto a sheet P fed from the sheet feed tray  8 . 
     The fixing unit  18  is disposed higher and further to the rear than the secondary transfer roller  41 . The fixing unit  18  includes a heat roller  48  and a pressing roller  49 . The pressing roller  49  presses a rear end portion of the heat roller  48 . The fixing unit  18  is configured to fix a color image transferred onto a sheet P thereon by heat while the sheet P having the color image passes between the heat roller  48  and the pressing roller  49 . 
     The discharge unit  5  protrudes upward from an upper rear end portion of the casing  2 . The discharge unit  5  includes an outlet  52  and a plurality of, for example, three, discharge rollers  53 . The outlet  52  allows a sheet P that has passed the fixing unit  18  to pass therethrough for discharging the sheet P onto the sheet discharge tray  54 . 
     The outlet  52  provides communication between the inside and the outside of the casing  2  at a front surface of the discharge unit  5 . 
     The discharge rollers  53  are disposed so as to pinch and guide a sheet P to be discharged through the outlet  52 . 
     The image reading unit  6  is disposed above the casing  2  so as to cover the sheet discharge tray  54 . The image reading unit  6  has a generally rectangular shape in plan view and has substantially the same dimensions in the front-rear direction and in a right-left direction as the casing  2 . The image reading unit  6  includes a document rest  56  and a retaining cover  57 . The document rest  56  is configured to support a document thereon. The retaining cover  57  is swingably supported by the document rest  56 . 
     The image forming unit  4  forms an image onto a sheet P based on image information read from a document by the image reading unit  6 . 
     2. Details of Process Cartridges 
     All of the process cartridges  14  have the same or similar configuration except color of toner stored therein, and therefore, one of the process cartridges  14  will be described in detail. 
     As depicted in  FIGS. 1 and 2 , a process cartridge  14  includes a cartridge frame  64 , a photosensitive drum  25 , a charging roller  30 , a developing unit  32 , and a drum cleaning unit  65 . 
     The process cartridge  14  is configured to move in the up-down direction (as an example of an orthogonal direction) between a first position (e.g., a position of the process cartridge  14  depicted in  FIGS. 1 and 2 ) and a second position (e.g., a position of the process cartridge  14  depicted in  FIG. 10 ). When the process cartridge  14  is located at the first position (refer to  FIGS. 1 and 2 ), a lower end portion of the photosensitive drum  25  is in contact with the outer surface of the upper portion of the intermediate transfer belt  44 . When the process cartridge  14  is located at the second position (refer to  FIG. 10 ), the photosensitive drum  25  is distanced from the outer surface of the upper portion of the intermediate transfer belt  44 . 
     (1) Cartridge Frame 
     As depicted in  FIGS. 1 and 3 , the cartridge frame  64  includes right and left side walls  67 , a bottom wall  68 , and a connecting bar  69 . 
     The right and left side walls  67  are spaced apart from each other in the right-left direction (as an example of an axial direction). The side walls  67  have a generally rectangular plate shape in side view and extend both in the up-down direction and in the front-rear direction. The left side wall  67  is an example of a first end portion of the process cartridge  14 , and the right side wall  67  is an example of a second end portion of the process cartridge. Both of the right and left side walls  67  have the same or similar configuration, and therefore, one of the right and left side walls  67  will be described in detail. As depicted in  FIGS. 2 and 3 , a side wall  67  has a flange support portion  70  and a through hole  71 . 
     The flange support portion  70  has a generally hollow cylindrical shape and protrudes toward the exterior of the printer  1  in the right-left direction from a lower front end of the side wall  67 . The flange support portion  70  penetrates the side wall  67 . The flange support portion  70  of the left side wall  67  has a cutout  72 . 
     The cutout  72  is recessed rightward relative to a lower left end portion of the flange support portion  70  of the left side wall  67  for exposing a lower end portion of a flange  27 . 
     The through hole  71  is defined in an upper rear end portion of the side wall  67  and is disposed higher and further to the rear than the flange support portion  70 . The through hole  71  has a generally circular shape in side view and penetrates the side wall  67 . 
     As depicted in  FIG. 1 , the bottom wall  68  extends between lower end portions of rear half portions of the side walls  67 . The bottom wall  68  has a generally rectangular plate shape in bottom view and extends both in the front-rear direction and in the right-left direction. 
     As depicted in  FIGS. 1 and 3 , the connecting bar  69  extends between front end portions of the side walls  67 . The connecting bar  69  is disposed at a position which is approximately ⅓ of a dimension in the up-down direction of the side wall  67  from an upper end of the side wall  67 . The connecting bar  69  has a generally rectangular bar shape in sectional view and extends in the right-left direction. The connecting bar  69  includes a handle  73  for a user to hold at the time of attaching or detaching the process cartridge  14  to or from the drawer  16 . 
     The handle  73  is disposed at a substantially middle portion of an upper surface of the connecting bar  69  in the right-left direction. The handle  73  has a generally inverted U-shaped plate in front view. 
     (2) Photosensitive Drum 
     As depicted in  FIGS. 1 and 2 , the photosensitive drum  25  is disposed at a lower end portion of the process cartridge  14  and at a substantially middle portion in the front-rear direction of the process cartridge  14 . As depicted in  FIG. 2 , the photosensitive drum  25  includes a drum  26  and right and left flanges  27 . 
     The drum  26  has a generally hollow cylindrical shape extending in the right-left direction. The drum  26  has a photosensitive layer on its surface. 
     One (e.g., the left flange  27 ) of the flanges  27  is disposed at a left end portion of the drum  26 , and the other (e.g., the right flange  27 ) of the flanges  27  is disposed at a right end portion of the drum  26 . The flanges  27  have a generally cylindrical column shape extending in the right-left direction. The flanges  27  have an outside diameter that is slightly smaller than an outside diameter of the drum  26 . The left flange  27  has gear teeth on its circumferential surface of a left end portion thereof. 
     The photosensitive drum  25  is rotatably supported by the right and left side walls  67  while the left flange  27  is supported by the flange support portion  70  of the left side wall  67  and the right flange  27  is supported by the flange support portion  70  of the right side wall  67 . A left end surface of the left flange  27  is flush with a left end surface of the left side wall  67  of the flange support portion  70  in the right-left direction. A right end surface of the right flange  27  is flush with a right end surface of the right side wall  67  of the flange support portion  70  in the right-left direction. A portion of a lower end portion of the left flange  27  is exposed through the cutout  72  of the flange support portion  70 . 
     (3) Charging Roller 
     As depicted in  FIG. 1 , the charging roller  30  has a generally cylindrical column shape extending in the right-left direction. The charging roller  30  is disposed diagonally above the photosensitive drum  25 . The center of the charging roller  30  is disposed further to the front than the center of the photosensitive drum  25 . A lower rear end portion of the charging roller  30  is in contact with an upper front end portion of the photosensitive drum  25 . The charging roller  30  is rotatably supported by the side walls  67  while a left end portion of the charging roller  30  is supported by the left side wall  67  and a right end portion of the charging roller  30  is supported by the right side wall  67 . 
     (4) Developing Unit 
     As depicted in  FIGS. 1 and 6 , the developing unit  32  is disposed higher and further to the rear than the photosensitive drum  25 . The developing unit  32  is configured to store toner therein. The developing unit  32  includes a developing frame  33 , a developing roller  34 , a supply roller  35 , a layer-thickness regulating blade  36 , a driving-force receiving member  37 , and an electrode member  38 . The driving-force receiving member  37  is configured to receive a driving force from the casing  2 . The electrode member  38  is configured to receive electric power from the casing  2 . 
     As depicted in  FIG. 1 , the developing frame  33  is disposed higher and further to the rear than the photosensitive drum  25  in a rear end portion of the process cartridge  14 . The developing frame  33  has a generally rectangular hollow cylindrical shape. The developing frame  33  extends in the right-left direction and has closed ends in the right-left direction. The developing frame  33  has an opening at a lower front end portion thereof. The opening extends in the right-left direction across a lower front end portion of the developing frame  33  so as to provide communication between the outside and the inside of the developing frame  33 . 
     The developing roller  34  is configured to supply toner onto a surface of the photosensitive drum  25 . The developing roller  34  has a generally cylindrical column shape extending in the right-left direction. The developing roller  34  is disposed in a lower front end portion of the developing frame  33 . A front end portion of the developing roller  34  is in contact with a rear end portion of the photosensitive drum  25 . 
     The supply roller  35  is configured to supply toner onto a surface of the developing roller  34  from the developing unit  32 . The supply roller  35  has a generally cylindrical column shape extending in the right-left direction and is disposed behind the developing roller  34 . A front end portion of the supply roller  35  is press contact with a rear end portion of the developing roller  34 . 
     The layer-thickness regulating blade  36  is configured to regulate a thickness of toner supplied onto the surface of the developing roller  34 . The layer-thickness regulating blade  36  is disposed higher and further to the rear than the developing roller  34 . The layer-thickness regulating blade  36  has a thickness in the front-rear direction and has a generally plate shape extending in the right-left direction. A lower end portion of the layer-thickness regulating blade  36  is in contact with an upper rear end portion of the developing roller  34 . 
     As depicted in  FIGS. 3 and 6 , the driving-force receiving member  37  is configured to transmit, to the developing roller  34  and the supply roller  35 , a driving force inputted thereto from a corresponding driving-force input member  130 . The driving-force receiving member  37  is disposed at an upper end portion of a left wall of the developing frame  33 . The driving-force receiving member  37  has a generally cylindrical column shape, and protrudes leftward relative to the left wall of the developing frame  33 . The driving-force receiving member  37  is disposed in the through hole  71  of the left side wall  67  while passing therethrough. That is, the driving-force receiving member  37  is supported by the left side wall  67 . Thus, the driving-force receiving member  37  is exposed through the through hole  71  when viewed from the left. The driving-force receiving member  37  has a hole  39  therein. 
     The hole  39  is recessed rightward relative to a left end of the driving-force receiving member  37  at a substantially middle portion of the driving-force receiving member  37  in left side view. The driving-force receiving member  37  has a generally circular shape in side view. 
     As depicted in  FIGS. 2 and 6 , the electrode member  38  is configured to supply the developing roller  34  and the supply roller  35  with electric power received from a corresponding electric-power supply member  132 . The electrode member  38  is disposed at an upper end portion of a right wall of the developing frame  33 . The electrode member  38  has a generally cylindrical column shape. The electrode member  38  protrudes rightward relative to the right wall of the developing frame  33 . The electrode member  38  is disposed in the through hole  71  of the right side wall  67  while passing therethrough. That is, the electrode member  38  is supported by the right side wall  67 . Thus, the electrode member  38  is exposed through the through hole  71  when viewed from the right. 
     (5) Drum Cleaning Unit 
     As depicted in  FIGS. 1 and 3 , the drum cleaning unit  65  is disposed in front of the photosensitive drum  25  in a lower front end portion of the process cartridge  14 . The drum cleaning unit  65  is configured to collect residual toner from the surface of the photosensitive drum  25 . The drum cleaning unit  65  includes a cleaning frame  76  and a cleaning blade  77 . 
     The cleaning frame  76  is disposed in front of the photosensitive drum  25  in the lower end portion of the process cartridge  14 . The cleaning frame  76  has a generally rectangular cylindrical shape extending in the right-left direction. A left end of the cleaning frame  76  is contiguous to an inner surface of the left side wall  67  in the right-left direction, and a right end of the cleaning frame  76  is contiguous to an inner surface of the right side wall  67  in the right-left direction. The cleaning frame  76  has an opening in a lower end portion of a rear wall so as to face a front end portion of the photosensitive drum  25 . The opening extends across the lower end portion of the rear wall of the cleaning frame  76  in the right-left direction and penetrates the cleaning frame  76  in the front-rear direction. 
     As depicted in  FIG. 1 , the cleaning blade  77  is disposed at a rear surface of the cleaning frame  76 . The cleaning blade  77  has a thickness in the front-rear direction and has a generally plate shape in the right-left direction. An upper end portion of the cleaning blade  77  is fixed to a lower end portion of the rear wall of the cleaning frame  76 . In other words, the upper end portion of the cleaning blade  77  is fixed to an upper circumferential edge portion of the opening that penetrates the rear wall of the cleaning frame  76  in the front-rear direction. A lower end portion of the cleaning blade  77  protrudes relative to a lower end of the rear wall of the cleaning blade  77  and extends to an approximately upper half of the opening of the cleaning frame  76 . A portion of the lower end portion of the cleaning blade  77  is in contact with a front end portion of the drum  26  of the photosensitive drum  25 . 
     3. Details of Drawer 
     The drawer  16  is configured to support all of the process cartridges  14 . The drawer  16  is configured to move in the front-rear direction between an inside position (e.g., a position of the drawer  16  depicted in  FIGS. 1 and 4 ) and an outside position (e.g., a position of the drawer  16  depicted in  FIG. 11 ). When the drawer  16  is located at the inside position (refer to  FIGS. 1 and 4 ), the drawer  16  is located inside the casing  2 . When the drawer  16  is located at the outside position (refer to  FIG. 11 ), the drawer  16  is located outside the casing  2 . The drawer  16  is further configured to move between an adjacent position (e.g., a position of the drawer  16  depicted in  FIG. 1 ) and a distant position (e.g., a position of the drawer  16  depicted in  FIG. 9 ) relative to the intermediate transfer belt  44  when the drawer  16  is located at the inside position. When the drawer  16  is located at the adjacent position (refer to  FIG. 1 ), the drawer  16  is located adjacent to the intermediate transfer belt  44 . When the drawer  16  is located at the distant position (refer to  FIG. 9 ), the drawer  16  is located at a position farther from the intermediate transfer belt  44  than the drawer  16  that is located at the adjacent position. 
     As depicted in  FIG. 3 , the drawer  16  includes a plate  85  (referred to herein as a bottom plate  85  that supports bottom wall  68  of cartridge frame  64 ), a plurality of, for example, four, rollers  89 , and a stopper  90 . 
     As depicted in  FIGS. 1 and 3 , the bottom plate  85  has a generally rectangular plate shape in plan view and extends both in the front-rear direction and in the right-left direction. The bottom plate  85  has an upper surface  86  and a lower surface  87 , and the upper surface  86  and the lower surface  87  are adjacent to each other in the up-down direction. The upper surface  86  of the bottom plate  85  is an example of a flat surface. The bottom plate  85  has no side plate that extends from its peripheral edges in the up-down direction. 
     As depicted in  FIGS. 2 and 3 , the bottom plate  85  includes a right end portion and a left end portion in the right-left direction. The bottom plate also includes a middle portion located between the right end portion and the left end portion. The lower surfaces of the right end portion and left end portion are higher than the lower surface of the middle portion across all cross-sectional views of the bottom plate  85  (except in the cross-sectional views across openings  91  as described herein). In other words, the right and left end portions of the bottom plate  85  have a thickness in the up-down direction that is thinner than the middle portion of the bottom plate  85 . The middle portion of the bottom plate  85  may be a thick plate portion  92  and the right and left end portions of the bottom plate  85  may be thin plate portions  93 . The left thin-plate portion  93  is an example of a first end portion of the bottom plate  85 . The right thin-plate portion  93  is an example of a second end portion of the bottom plate  85 . 
     The bottom plate  85  has a plurality of, for example, four, recessed portions  88  and a plurality of, for example, four, openings  91 . 
     The recessed portions  88  are spaced apart from each other in the front-rear direction. The recessed portions  88  are recessed downward relative to the upper surface  86  of the bottom plate  85 . The recessed portions  88  have a generally rectangular shape in plan view extending across the thick plate portion  92  in the right-left direction. 
     Each of the openings  91  is defined in a corresponding one of the recessed portions  88  and penetrates the bottom plate  85  in the up-down direction while being slightly spaced rearward from a front end of a corresponding one of the recessed portions  88 . The openings  91  have a length that is longer than the recessed portions  88  such that right and left edges of the openings  91  are located closer to the exterior of the printer  1  than right and left edges of the recessed portions  88 , respectively, in the right-left direction. The openings  91  have a generally rectangular shape in plan view and are elongated to the right and left thin plate portions  93 . 
     The recessed portions  88  each have an up-facing surface that may be a support surface  94  for supporting a corresponding process cartridge  14 . 
     Two of the rollers  89  are disposed side by side in the front-rear direction at a rear end portion of a left end of the drawer  16 , and the other two of the rollers  89  are disposed side by side in the front-rear direction at a rear end portion of a right end of the drawer  16 . The rollers  89  are configured to rotate on respective axes extending in the right-left direction. 
     The stopper  90  is disposed at a front end of the drawer  16 . The stopper  90  includes a shaft portion  96  and a projecting portion  97 . 
     The shaft portion  96  has a generally cylindrical column shape and protrudes rearward from a substantially middle portion in the right-left direction of a front end portion of the bottom plate  85 . The shaft portion  96  is configured to rotate relative to the bottom plate  85 . 
     The projecting portion  97  has a generally rectangular column shape. The projecting portion  97  extends from a portion of a periphery of the shaft portion  96  in a diameter direction of the shaft portion  96  toward the exterior of the printer  1 . 
     With this configuration, the stopper  90  is configured to rotate on the shaft portion  96  between a restricting position and a non-restricting position. When the stopper  90  is located at the restricting position (e.g., a position of the stopper  90  indicated by a solid line in  FIG. 3 ), the projecting portion  97  extends downward such that the projecting portion  97  is located below the lower surface  87  of the bottom plate  85  to restrict a movement of the drawer  16  in the front-rear direction. When the stopper  90  is located at the non-restricting position (e.g., a position of the stopper  90  indicated by a double-dotted and dashed line in  FIG. 3 ), the projecting portion  97  extends rightward and is located between the upper surface  86  and the lower surface  87  of the bottom plate  85  in the up-down direction to permit the drawer  16  to move in the front-rear direction. 
     As depicted in  FIG. 4 , a dimension in the up-down direction H 1  of the bottom plate  85  is smaller than a dimension in the up-down direction H 2  of the process cartridge  14 . More specifically, the dimension in the up-down direction H 1  of the bottom plate  85  may be between 3% and 30% inclusive, preferably between 5% and 10% inclusive, of the dimension in the up-down direction H 2  of the process cartridge  14 . 
     A dimension in the up-down direction H 3  of the recessed portion  88  is smaller than the dimension in the up-down direction H 2  of the process cartridge  14 . More specifically, the dimension in the up-down direction H 3  of the recessed portion  88  may be 10% or less, preferably between 2% and 8% inclusive, of the dimension in the up-down direction H 2  of the process cartridge  14 . All of the recessed portions  88  have the same dimension in the up-down direction. 
     A dimension in the up-down direction H 1  of the bottom plate  85  is smaller than a dimension in the up-down direction H 4  of the driving-force receiving member  37 . More specifically, the dimension in the up-down direction H 1  of the bottom plate  85  may be between 30% and 90% inclusive, preferably between 50% and 70% inclusive, of the dimension in the up-down direction H 4  of the driving-force receiving member  37 . 
     4. Details of Casing 
     (1) Configuration of Belt Cleaning Unit of Casing 
     As depicted in  FIGS. 1 and 4 , the casing  2  includes a belt cleaning unit  100 . 
     The belt cleaning unit  100  includes a cleaning frame  101 , a cleaning blade  102 , a brush roller  103 , a screw  104 , a connecting tube  105 , a screw  106 , and a residual toner box  107 . 
     The cleaning frame  101  is disposed above the drive roller  42  while the cleaning frame  101  and the drive roller  42  sandwiches the intermediate transfer belt  44  therebetween. The cleaning frame  101  includes an accommodating portion  109  that accommodates the brush roller  103  therein and an accommodating portion  110  that accommodates the screw  104  therein. 
     The accommodating portion  109  has a generally hollow cylindrical shape. The accommodating portion  109  extends in the right-left direction and has closed ends in the right-left direction. The accommodating portion  109  has an opening in a lower end portion thereof. The opening is elongated across the lower end portion of the accommodating portion  109  in the right-left direction and penetrates the accommodating portion  109  in the up-down direction. 
     As depicted in  FIG. 1 , the accommodating portion  110  has a generally hollow cylindrical shape. The accommodating portion  110  extends in the right-left direction and has a closed left end. The accommodating portion  110  is disposed in front of the accommodating portion  109  such that the inside of the accommodating portion  110  is in communication with the inside of the accommodating portion  109 . A diameter of the accommodating portion  110  is smaller than a diameter of the accommodating portion  109 . 
     The cleaning blade  102  is disposed at a lower front end portion of the accommodating portion  109 . The cleaning blade  102  has a thickness in an obliquely downward direction from its upper surface toward the front. The cleaning blade  102  has a generally plate shape extending in the right-left direction. The accommodating portion  109  has an opening that penetrates a lower end portion thereof so as to provide communication between the inside and the outside of the accommodating portion  109 . An upper front portion of the cleaning blade  102  is fixed to a front circumferential edge portion of the opening of the accommodating portion  109 . A lower rear portion of the cleaning blade  102  protrudes relative to a front end of the front circumferential edge portion of the opening and extends to an approximately front half of the opening of the accommodating portion  109 . A lower rear end portion of the cleaning blade  102  is in contact with an upper rear end portion of the intermediate transfer belt  44 . 
     The brush roller  103  is disposed inside the accommodating portion  109 . The brush roller  103  extends in the right-left direction and has hair-like pieces or bristles on its surface. 
     The screw  104  is disposed inside the accommodating portion  110 . The screw  104  may be an auger screw extending in the right-left direction. 
     As depicted in  FIGS. 1 and 4 , the connecting tube  105  extends obliquely downward toward the front. The connecting tube  105  has a generally hollow cylindrical shape having a closed upper end and a closed lower end. The connecting tube  105  has an opening that penetrates a right wall of an upper end portion thereof in the right-left direction. The upper end portion of the connecting tube  105  is connected to a right end portion of the accommodating portion  110 . Thus, the inside of the connecting tube  105  is in communication with the inside of the accommodating portion  110 . The connecting tube  105  has another opening that penetrates a left wall of a lower end portion thereof in the right-left direction. 
     The screw  106  is disposed in the lower end portion of the connecting tube  105 . The screw  106  may be an auger screw extending in the right-left direction. 
     The residual toner box  107  has a protruding portion protruding upward at an upper end portion. The residual toner box  107  has a generally box shape extending both in the up-down direction and in the front-rear direction. The residual toner box  107  has an opening that penetrates a right wall of the protruding portion in the right-left direction. The protruding portion of the residual toner box  107  is connected to the lower end portion of the connecting tube  105 . Thus, the inside of the residual toner box  107  is in communication with the inside of the connecting tube  105 . 
     (2) Configuration of Frames of Casing 
     As depicted in  FIG. 2 , the casing  2  includes right and left side plates  111 , right and left frames  112 , upper and lower connecting plates  113 , right and left positioning plates  114 , and right and left base portions  115 . 
     As depicted in  FIGS. 2 and 6 , the side plates  111  are spaced apart from each other in the right-left direction. The side plates  111  have a generally rectangular plate shape in side view and extend in the front-rear direction. The left side plate  111  is an example of a first side plate. The right side plate  111  is an example of a second side plate. 
     The right and left frames  112  are disposed closer to the center of the printer  1  than the right and left side plates  111 , respectively. That is, the right and left frames  112  are disposed between the right and left side plates  111 . The frames  112  have a generally box shape. An outer end portion of each frame  12  in the right-left direction is contiguous to an inner surface of a corresponding one of the side plates  111 , thereby defining an accommodation space  117 . 
     As depicted in  FIG. 1  and  FIG. 2 , one (e.g., the upper connecting plate  113 ) of the connecting plates  113  is disposed extending between an upper end portion of the right side plate  111  and an upper end portion of the left side plates  111 . The other (e.g., the lower connecting plate  113 ) of the connecting plates  113  is disposed extending between a lower end portion of the right side plate  111  and a lower end portion of the left side plate  111 . The upper connecting plate  113  is disposed below the exposing device  15  in an upper portion of the casing  2 . The upper connecting plate  113  has a generally rectangular plate shape in plan view in the front-rear direction. The lower connecting plate  113  is disposed below the belt unit  40  in a lower portion of the casing  2 . The lower connecting plate  113  has a generally rectangular plate shape in plan view. The lower connecting plate  113  is inclined upward toward the front so as to extend along a lower portion of the intermediate transfer belt  44 . 
     As depicted in  FIGS. 2 and 4 , one (e.g., the left positioning plate  114 ) of the positioning plates  114  is disposed on an upper surface of the lower connecting plate  113  and to the left of the belt unit  40 . The other (e.g., the right positioning plate  114 ) of the positioning plates  114  is disposed on the upper surface of the lower connecting plate  113  and to the right of the belt unit  40 . The positioning plates  114  have a generally rectangular plate shape in side view extending in the front-rear direction. Lower end portions of the positioning plates  114  are bent toward the right. Lower ends of the positioning plates  114  are inclined upward toward the front along the inclined lower connecting plate  113 . Upper ends of the positioning plates  114  extend along the front-rear direction. The positioning plates  114  each have a plurality of, for example, four, positioning recesses  121 . 
     As depicted in  FIG. 4 , the positioning recesses  121  are arranged side by side in the front-rear direction while being spaced apart from each other in the front-rear direction. The positioning recesses  121  are recessed downward relative to the upper end of the positioning plate  114  and have a generally arc shape in side view. The positioning recesses  121  each have a shape corresponding to the periphery of a corresponding flange support portion  70  of the cartridge frame  64 . 
     As depicted in  FIGS. 2 and 5 , one (e.g., the left base portion  115 ) of the base portions  115  is disposed on the upper surface of the lower connecting plate  113  and to the left of the left positioning plate  114 . The other (e.g., the right base portion  115 ) of the base portions  115  is disposed on the upper surface of the lower connecting plate  113  and to the right of the right positioning plate  114 . The base portions  115  have a generally rectangular thick plate shape in side view extending in the front-rear direction. Lower ends of the base portions  115  extend obliquely upward toward the front along the inclined lower connecting plate  113 . Upper ends of the base portions  115  extend along the front-rear direction. The base portions  115  each include a plurality of, for example, five, base shafts  123 . The left base portion  115  further includes a plurality of, for example, four, drum gears  124  and a plurality of, for example, four, drum gear shafts  125 . 
     As depicted in  FIG. 5 , the base shafts  123  are disposed at an upper end portion of a substantially middle portion in the right-left direction of the base portions  115 . The base shafts  123  are arranged side by side in the front-rear direction while being spaced apart from each other in the front-rear direction. The base shafts  123  have a generally cylindrical column shape extending in the right-left direction. 
     As depicted in  FIG. 4 , the drum gears  124  are spaced apart from each other in the front-rear direction. As depicted in  FIGS. 2 and 4 , the drum gears  124  are disposed below the left flanges  27  of the photosensitive drums  25 , respectively, in a state where the process cartridges  14  are located inside the casing  2 . As described above, the lower end portions of the left flanges  27  of the photosensitive drums  25  are not covered by the respective flange support portions  70 . 
     The drum gear shafts  125  extend in the right-left direction from the left base portion  115  toward the centers of the drum gears  124 , respectively. The drum gear shafts  125  have a generally cylindrical column shape. Each of the drum gear shafts  125  passes through a middle portion of a corresponding drum gear  124  in its diameter direction so as not to rotate relative to the drum gear  124 . 
     This configuration may enable transmission of driving force from a drive source (not depicted) to the drum gears  124  via the respective drum gear shafts  125 . 
     (3) Configuration for Inputting Driving Force and Supplying Electric Power to Developing Units of Casing 
     As depicted in  FIGS. 2 and 6 , the casing  2  further includes a plurality of, for example, four, driving-force input members  130 , a power supply board  131 , a plurality of, for example, four, electric-power supply members  132 , and right and left movable members  133 . 
     The driving-force input members  130  are spaced apart from each other in the front-rear direction such that the driving-force input members  130  are positioned to the left of the respective driving-force receiving members  37 . All of the driving-force input members  130  have the same or similar configuration, and therefore, one of the driving-force input members  130  will be described in detail. A driving-force input member  130  has a body portion  136 , a spring  137 , and an input gear  138 . 
     The body portion  136  has a generally cylindrical column shape extending in the right-left direction. The body portion  136  has a left end portion DE 1  and a right end portion DE 2 . The body portion  136  penetrates the left side plate  111  and the left frame  112  in the right-left direction. Therefore, the left end portion DE 1  of the body portion  136  is located further to the left than the left side plate  111  and the right end portion DE 2  of the body portion  136  is located further to the right than the left frame  112 . That is, a middle portion of the body portion  136  in the right-left direction is located within the accommodation space  117  defined by the left side plate  111  and the left frame  112 . The left end portion DE 1  of the body portion  136  is an example of a first end portion of the driving-force input member  130 . The right end portion DE 2  of the body portion  136  is an example of a second end portion of the driving-force input member  130 . That is, as depicted in  FIG. 10 , the right end portion DE 2  of the driving-force input member  130  is located between the left guide rail  185  and the right guide rail  185  when viewed in the up-down direction in a state where the driving-force input member  130  is located at a disengaged position. As depicted in  FIGS. 2 and 6 , the body portion  136  includes an annular portion  139 . 
     The annular portion  139  has a generally ring shape. The annular portion  139  protrudes from a substantially middle portion of the body portion  136  in the right-left direction, e.g., a portion of the body portion  136  located within the accommodation space  117 , toward the exterior of the printer  1  in a diameter direction of the body portion  136  and extends in its circumferential direction. 
     The spring  137  may be a coil-shaped spring of a helically wound wire extending along the right-left direction. The spring  137  is attached to the body portion  136  in a contracted state while one end portion of the spring  137  is in contact with the left side plate  111  and the other end portion of the spring  137  is in contact with the annular portion  139 . Therefore, the spring  137  urges the body portion  136  rightward at all times. 
     The input gear  138  is disposed at a left surface of the left side plate  111 . The input gear  138  has a generally cylindrical shape extending in the right-left direction. The input gear  138  includes a flange portion that protrudes from a right end portion of the input gear  138  in its diameter direction and extends in its circumferential direction. The flange portion of the right end portion of the input gear  138  has gear teeth on its circumferential surface. The input gear  138  accommodates a portion of the body portion  136  therein and is capable of transmitting a driving force from the drive source (not depicted) to the body portion  136 . 
     The driving-force input member  130  is configured to move in the right-left direction between an engaged position (e.g., a position of the driving-force input member  130  depicted in  FIGS. 2 and 6 ) and a disengaged position (e.g., a position of the driving-force input member  130  depicted in  FIGS. 8 and 10 ). When the driving-force input member  130  is located at the engaged position (refer to  FIGS. 2 and 6 ), the driving-force input member  130  is able to transmit a driving force from the drive source (not depicted) to a corresponding developing unit  32 . When the driving-force input member  130  is located at the disengaged position (refer to  FIGS. 8 and 10 ), the driving-force input member  130  does not transmit a driving force to the corresponding developing unit  32 . The driving-force input member  130  located at the engaged position is configured to be able to input a driving force to the corresponding driving-force receiving member  37  while being in engagement with the corresponding driving-force receiving member  37 . The driving-force input member  130  located at the disengaged position is configured not to engage with the corresponding driving-force receiving member  37 . 
     As depicted in  FIGS. 2 and 6 , the power supply board  131  is disposed adjacent to the right side plate  111  in the right accommodation space  117 . The power supply board  131  has a generally rectangular plate shape in side view extending in the front-rear direction. The power supply board  131  may be a circuit board including, for example, a transformer and a capacitor. The power supply board  131  is configured to amplify voltage supplied from an input power source (not depicted) using the transformer and store the amplified voltage in the capacitor. The power supply board  131  is further configured to supply electric power to the electric-power supply members  132 . 
     The electric-power supply members  132  are disposed to the right of the respective electrode members  38  while being spaced apart from each other in the front-rear direction. All of the electric-power supply members  132  have the same or similar configuration, and therefore, one of the electric-power supply members  132  will be described in detail. An electric-power supply member  132  has a fixed portion  145 , a body portion  142 , and a spring  143 . 
     The fixed portion  145  has a generally cylindrical column shape extending in the right-left direction. The fixed portion  145  has a right end portion PE 1 . The fixed portion  145  is supported by the right side plate  111  while the right end portion PE 1  penetrates and protrudes from the power supply board  131 . The right end portion PE 1  of the fixed portion  145  is an example of a first end portion of the electric-power supply member  132 . 
     The body portion  142  extends in the right-left direction and has a generally cylindrical shape with its left end closed. The body portion  142  is attached to the fixed portion  145  from the left and penetrates the right frame  112  in the right-left direction. The body portion  142  has a left end portion PE 2 . While a right end portion of the body portion  142  is positioned within the accommodation space  117 , the left end portion PE 2  of the body portion  142  is located further to the left than the right frame  112 . The left end portion PE 2  is an example of a second end portion of the body portion  142 . That is, as depicted in  FIG. 10 , the left end portion PE 2  of the electric-power supply member  132  is located between the left guide rail  185  and the right guide rail  185  when viewed in the up-down direction in a state where the electric-power supply member  132  is located at a non-contacting position. As depicted in  FIGS. 2 and 6 , the body portion  142  includes an annular portion  144 . 
     The annular portion  144  has a generally ring shape. The annular portion  144  protrudes from a right end portion of the body portion  142 , e.g., a portion of the body portion  142  located within the accommodation space  117 , toward the exterior of the printer  1  in a diameter direction of the body portion  142  and extends in its circumferential direction. 
     The spring  143  has conductivity. The spring  143  may be a coil-shaped spring of a helically wound wire extending along the right-left direction. The spring  143  is attached to the fixed portion  145  in a contracted state while one end portion of the spring  142  is in contact with the power supply board  131  and the other end portion of the spring  142  is in contact with the annular portion  144 . Therefore, the spring  143  urges the body portion  142  leftward at all times. 
     The electric-power supply member  132  is configured to move between a contacting position (e.g., a position of the electric-power supply member  132  depicted in  FIGS. 2 and 6 ) and a non-contacting position (e.g., a position of the electric-power supply member  132  depicted in  FIGS. 8 and 10 ). When the electric-power supply member  132  is located at the contacting position (refer to  FIGS. 2 and 6 ), the electric-power supply member  132  is in contact with a corresponding electrode member  38 . When the electric-power supply member  132  is located at the non-contacting position (refer to  FIGS. 8 and 10 ), the electric-power supply member  132  is not in contact with the corresponding electrode member  38 . The electric-power supply member  132  located at the contacting position is configured to supply electric power to the corresponding electrode member  38  while being in contact with the corresponding electrode member  38 . The electric-power supply member  132  located at the non-contacting position is configured to not contact with the corresponding electrode member  38 . 
     As depicted in  FIGS. 2 and 6 , one (e.g., the left movable member  133 ) of the movable members  133  is disposed within the left accommodation space  117 , and the other (e.g., the right movable member  133 ) of the movable members  133  is disposed within the right accommodation space  117 . Both of the movable members  133  have the same or similar configuration, and therefore, one of the movable members  133  will be described in detail. A movable member  133  has a translation cam  147  and a spring  148 . 
     The translation cam  147  has a generally plate shape extending in the front-rear direction. The translation cam  147  includes a plurality of, for example, four, protruding portions  150 , a plurality of, for example, four, inclined portions  151 , and an accommodating portion  153 . The translation cam  147  further has a plurality of, for example, four, elongated holes  152  therein. 
     The protruding portions  150  are spaced apart from each other in the front-rear direction. Spacing between each protruding portion  150  in the front-rear direction in the translation cam  147  of the left movable member  133  is the same as spacing between each driving-force receiving member  37  in the front-rear direction. Spacing between each protruding portion  150  in the front-rear direction in the right translation cam  147  of the right movable member  133  is the same as spacing between each electrode member  38  in the front-rear direction. The protruding portions  150  have a generally rectangular shape. The protruding portions  150  protrude from an outer surface of the translation cam  147  of the movable member  133  toward the exterior of the printer  1  in the right-left direction. 
     Each of the inclined portions  151  is inclined toward the center of the printer  1  in the right-left direction from a front end of a corresponding protruding portions  150 . The inclined portions  151  have a generally triangular shape in plan view and are contiguous to the outer surface of the translation cam  147  in the right-left direction. 
     As depicted in  FIGS. 5 and 6 , the elongated holes  152  are spaced apart from each other in the front-rear direction and penetrate the translation cam  147  in the right-left direction. More specifically, each of the elongated holes  152  is elongated frontward from a rear end of a corresponding one of the protruding portions  150  in side view. The elongated hole  152  is elongated to a position further to the front than a corresponding inclined portion  151 . 
     The accommodating portion  153  is recessed frontward relative to a rear end surface of the translation cam  147 . The accommodating portion  153  has a generally rectangular shape in rear view. 
     The spring  148  may be a coil-shaped spring of a helically wound wire extending along the front-rear direction. The spring  148  is disposed in a contracted state in the accommodating portion  153  while one end portion of the spring  148  is in contact with a front surface of the accommodating portion  153  and the other end portion of the spring  148  is in contact with a rear wall of the frame  112 . Therefore, the spring  148  urges the translation cam  147  frontward at all times. 
     The right movable member  133  is configured to move between in the front-rear direction between a driving-force supply side first position (e.g., a position of the right movable member  133  depicted in  FIGS. 2 and 6 ) and a driving-force supply side second position (e.g., a position of the right movable member  133  depicted in  FIGS. 8 and 10 ). When the right movable member  133  is located at the driving-force supply side first position, the right movable member  133  retains the driving-force input members  130  at the engaged position. When the right movable member  133  is located at the driving-force supply side second position, the right movable member  133  retains the driving-force input members  130  at the disengaged position. The right movable member  133  is an example of a first movable member. 
     The left movable member  133  is configured to move in the front-rear direction between an electric-power supply side first position (e.g., a position of the left movable member  133  depicted in  FIGS. 2 and 6 ) and an electric-power supply side second position (e.g., a position of the left movable member  133  depicted in  FIGS. 8 and 10 ). When the left movable member  133  is located at the electric-power supply side first position, the left movable member  133  retains the electric-power supply members  132  at the contacting position. When the left movable member  133  is located at the electric-power supply side second position, the left movable member  133  retains the electric-power supply members  132  at the non-contacting position. The left movable member  133  is an example of a second movable member. 
     (4) Configuration for Moving Drawer relative to Casing 
     As depicted in  FIGS. 2 and 5 , the casing  2  further includes a guide unit  183  and an engagement portion  186 . 
     The guide unit  183  includes right and left guide rails  185  and a plurality of link portions  184 . The link portions  184  are grouped into five pairs, and each pair includes a right link portion  184  and a left link portion  184 . 
     One (e.g., the left guide rail  185 ) of the guide rails  185  is disposed below the left frame  112  and above the left base portion  115  while being disposed further to the right than the left side plate  111 . The other (e.g., the right guide rail  185 ) of the guide rails  185  is disposed below the right frame  112  and above the right base portion  115  while being disposed further to the left than the right side plate  111 . Both of the right and left guide rails  185  have the same or similar configuration, and therefore, one of the guide rails  185  will be described in detail. A guide rail  185  has a generally rectangular column shape in the front-rear direction. As depicted in  FIGS. 2 and 9 , the guide rail  185  has a first guide groove  188  and a second guide groove  189  and further includes a plurality of, for example, two, rollers  190 , an engagement shaft  191 , and a plurality of, for example, five, guide rail shafts  192 . 
     The first guide groove  188  is recessed relative to an inner surface of the guide rail  185  in the right-left direction toward the exterior of the printer  1  in the right-left direction (e.g., rightward or leftward). The first guide groove  188  extends from a rear end portion of the guide rail  185  to a front end of the guide rail  185  so as to have an opening at its front end. The first guide groove  188  has a generally rectangular shape in sectional view. 
     As depicted in  FIG. 2 , the second guide groove  189  is recessed relative to an inner surface (e.g., a right surface or a left surface) of the first guide groove  188  in the right-left direction toward the exterior of the printer  1  in the right-left direction (e.g., rightward or leftward) at a substantially middle portion of the first guide groove  188  in the up-down direction. The second guide groove  189  extends from a rear end portion of the guide rail  185  to the front end of the guide rail  185  so as to have an opening at its front end. The second guide groove  189  has a generally rectangular shape in sectional view. 
     As depicted in  FIGS. 2 and 5 , the rollers  190  are configured to rotate on respective axes extending in the right-left direction. The rollers  190  are disposed such that their upper end portions are located higher than a lower surface of a front end portion of the first guide groove  188 . The rollers  190  are disposed side by side in the front-rear direction. 
     As depicted in  FIG. 9 , the engagement shaft  191  has a generally cylindrical column shape. The engagement shaft  191  protrudes from an outer surface (e.g., a right surface or a left surface) of the front end portion of the guide rail  185  in the right-left direction toward the exterior of the printer  1  in the right-left direction (e.g., rightward or leftward). The engagement shafts  191  of the guide rails  185  are in engagement with movable end portions of an interlock portion  202  of the front cover  7 . 
     As depicted in  FIGS. 5 and 9 , the guide rail shafts  192  are spaced apart from each other in the front-rear direction at a lower end portion of a substantially middle portion of the guide rail  185  in the right-left direction. The guide rail shafts  192  have a generally cylindrical column shape extending in the right-left direction. Spacing between each guide rail shaft  192  in the front-rear direction is the same as spacing between each base shafts  123  in the front-rear direction. 
     The left guide rail  185  is an example of a first guide member. The right guide rail  185  is an example of a second guide member. 
     The paired link portions  184  are spaced apart from each other in the front-rear direction. The link portions  184  have generally bar shape extending obliquely downward toward the front in a state where the process cartridges  14  are located at the first position as depicted in  FIG. 5 . Each of the link portions  184  has an opening having a generally circular shape in side view. Each of the openings penetrates one end portion of a corresponding link portion  184  and allows a corresponding base shaft  123  to pass therethrough such that the base shaft  123  is rotatable relative to the link portion  184 . Each of the link portions  184  has another opening having a generally circular shape in side view. Each of the openings penetrates the other end portion of the corresponding link portion  184  and allows a corresponding guide rail shaft  192  to pass therethrough such that the guide rail shaft  192  is rotatable relative to the link portion  184 . 
     As depicted in  FIG. 1 , the engagement portion  186  is disposed at a substantially middle portion in the right-left direction between the right and left guide rails  185 . The engagement portion  186  has a generally thick plate shape having a generally U-shaped cutout in side view. The engagement portion  186  has an upper open end. 
     As depicted in  FIGS. 1 and 5 , the front cover  7  includes a body portion  200 , a manual feed tray  201 , and the interlock portion  202 . 
     The body portion  200  has a generally rectangular plate shape in front view extending in the up-down direction. The body portion  200  includes an inclined portion at its upper end portion. The inclined portion of the body portion  200  is inclined toward the rear. The body portion  200  has a size that is capable of closing the opening  20 . As depicted in  FIGS. 5 and 6 , the body portion  200  includes right and left protrusions  203 . 
     The right and left protrusions  203  are spaced apart from each other in the right-left direction. Spacing between the right and left protrusions  203  in the right-left direction is substantially the same as spacing between the right and left translation cams  147  in the right-left direction. The protrusions  203  have a generally trapezoidal plate shape in side view and protrude rearward from a rear surface of the body portion  200 . 
     As depicted in  FIG. 1 , the manual feed tray  201  is disposed at a substantially middle portion of the body portion  200  in the up-down direction. The manual feed tray  201  has a generally rectangular plate shape in side view extending in the right-left direction. The manual feed tray  201  is configured to pivot on a lower end portion of the body portion  200  and tilt toward the front from an upright position. 
     As depicted in  FIGS. 7 and 9 , the interlock portion  202  has a generally bar shape. The interlock portion  202  is capable of bending at a substantially middle portion thereof in its longitudinal direction. The interlock portion  202  has base ends connected to a substantially middle portion of the body portion  200  in the up-down direction. As described above, the movable end portions of the interlock portion  202  are in engagement with the engagement shafts  191  of the guide rails  185 , respectively. 
     5. Installed State of Process Cartridges in Casing 
     As depicted in  FIGS. 1 and 4 , in a state where all of the process cartridges  14  are installed in the casing  2 , the drawer  16  is located at the adjacent position of the inside position, the stopper  90  is located at the restricting position, the process cartridges  14  are located at the first position, and the front cover  7  is located at the closing position. 
     Further, the driving-force input members  130  are located at the engaged position, the left movable member  133  is located at the driving-force supply side first position, the electric-power supply members  132  are located at the contacting position, and the right movable member  133  is located at the electric-power supply side second position. 
     The process cartridges  14  are placed on the support surfaces  94  of the recessed portions  88 , respectively, of the bottom plate  85 . More specifically, the process cartridges  14  are supported by the support surfaces  94  of the recessed portions  88 , respectively, such that the lower end portions of the photosensitive drums  25  protrude through the respective openings  91 . Thus, the process cartridges  14  are left exposed from the bottom plate  85  in side view. 
     As depicted in  FIG. 4 , of a projected plane of a process cartridge  14  in side view, an area of a portion that overlaps the bottom plate  85  may be between 3% and 30% inclusive, preferably between 5% and 10% inclusive, of a total area of the projected plane of the process cartridge  14 . The projected plane of the process cartridge refers to an area based on a projection of the process cartridge onto a virtual plane that is perpendicular to the axial direction. Similar projected planes are applicable to the drawer, bottom plate, and other structures. 
     As depicted in  FIG. 2 , the drawer  16  is located inside the casing  2  while being supported such that the left thin-plate portion  93  is received by the first guide groove  188  of the left guide rail  185 , the right thin-plate portion  93  is received by the first guide groove  188  of the right guide rail  185 , the left rollers  89  are received by the second guide groove  189  of the left guide rail  185 , and the right rollers  89  are received by the second guide groove  189  of the right guide rail  185 . 
     In this state, the driving-force input members  130  and the electric-power supply members  132  are located above the bottom plate  85 . 
     The left movable member  133  overlaps the left thin-plate portion  93  of the bottom plate  85  when projected in the up-down direction. The right movable member  133  overlaps the right thin-plate portion  93  of the bottom plate  85  when projected in the up-down direction. 
     The stopper  90  of the drawer  16  is located at the restricting position. Thus, the projecting portion  97  is in engagement with the engagement portion  186  to restrict movement of the drawer  16  in the front-rear direction. 
     As depicted in  FIG. 5 , the drawer  16  supporting the process cartridges  14  is located adjacent to the intermediate transfer belt  44  (e.g., at the adjacent position) by its own weight. In this state, the link portions  184  extend upward and rearward from the respective base shafts  123 . 
     As depicted in  FIGS. 2 and 4 , the flange support portions  70  of the process cartridges  14  are engaged with the respective positioning recesses  121  of the positioning plate  114 . 
     The lower portions of the left flanges  27  of the photosensitive drums  25  are in mesh with the upper end portions of the drum gears  124 , respectively. 
     As described above, the photosensitive drums  25  are placed at their positions by the right and left positioning plates  114  such that the photosensitive drums  25  are in contact with the outer surface of the upper portion of the intermediate transfer belt  44 . 
     As depicted in  FIGS. 5 and 6 , the front cover  7  is located at the closing position. In this state, the front end portion of the translation cam  147  of the left movable member  133  is in contact with the left protrusion  203 , whereby the translation cam  147  of the left movable member  133  is located at a rearward position against an urging force of the spring  148 . The front end portion of the translation cam  147  of the right movable member  133  is also in contact with the right protrusion  203 , whereby the translation cam  147  of the right movable member  133  is located at a rearward position against an urging force of the spring  148 . 
     Thus, as depicted in  FIG. 6 , the body portion  136  of each of the driving-force input members  130  is positioned at a front end portion of a corresponding one of the elongated holes  152  of the left translation cam  147 . In this state, each of the driving-force input members  130  is in engagement with the hole  39  of a corresponding one of the driving-force receiving members  37  by application of an urging force to each of the body portions  136  by a corresponding one of the springs  137 . 
     The body portion  142  of each of the electric-power supply members  132  is positioned at a front end portion of a corresponding one of the elongated holes  152  of the right translation cam  147 . In this state, the left end portion PE 2  of the body portion  142  of each of the electric-power supply members  132  is in contact with the electrode member  38  of a corresponding one of the process cartridges  14  by application of an urging force to each of the body portions  142  by a corresponding one of the springs  143 . 
     6. Procedure for Detaching Process Cartridges 
     (1) Opening of Front Cover 
     In order to detach a process cartridge  14  from the casing  2 , as depicted in  FIG. 7 , the front cover  7  is pivoted from the closing position toward the exposing position. In response to this, the left protrusion  203  of the front cover  7  is disengaged from the front end of the translation cam  147  of the left movable member  133  and the right protrusion  203  of the front cover  7  is disengaged from the front end of the translation cam  147  of the right movable member  133 . 
     Thus, the left translation cam  147  is moved frontward by an urging force of the left spring  148 , and therefore, as depicted in  FIG. 8 , the left movable member  133  is located at the driving-force supply side second position. Further, the right translation cam  147  is moved frontward by an urging force of the right spring  148 , and therefore, the right movable member  133  is located at the electric-power supply side second position. 
     While the left translation cam  147  is moved as described above, the left translation cam  147  moves the body portions  136  of the driving-force input members  130  leftward against the urging force of the respective springs  137  such that the left translation cam  147  causes the annular portions  139  of the driving-force input members  130  to slide over the respective inclined portions  151 . 
     Therefore, the annular portions  139  of the driving-force input members  130  are positioned in contact with the left surfaces of the protruding portions  150 , respectively. 
     In this state, as depicted in  FIG. 10 , the right end portion DE 2  of the body portion  136  of each of the driving-force input members  130  is located further to the right than the left guide rail  185  and overlaps the left end portion of the thick plate portion  92  of the bottom plate  85  when projected in the up-down direction. 
     As described above, the body portions  136  are disengaged from the respective holes  39  and the driving-force input members  130  are located at the disengaged position. In other words, in a state where the driving-force input members  130  are located at the disengaged position, the right end portions DE 2  of the body portions  136  are located between the right and left guide rails  185  when projected in the up-down direction. 
     While the right translation cam  147  is moved as described above, the right translation cam  147  moves the body portions  142  of the electric-power supply members  132  rightward against the urging force of the respective springs  143  such that the right translation cam  147  causes the annular portions  144  of the electric-power supply members  132  to slide over the respective inclined portions  151 . 
     Therefore, the annular portions  144  of the electric-power supply members  132  are positioned in contact with the right surfaces of respective protruding portions  150 . 
     In this state, as depicted in  FIG. 10 , the left end portion PE 2  of the body portion  142  of each of the electric-power supply members  132  is located further to the left than the right guide rail  185  and overlaps the right end portion of the thick plate portion  92  of the bottom plate  85  when projected in the up-down direction. 
     As described above, the body portions  142  are separated from the respective electrode members  38  and the electric-power supply members  132  are located at the non-contacting position. In other words, in a state where the electric-power supply members  132  are located at the non-contacting position, the left end portion PE 2  of the body portion  142  is located between the right and left guide rails  185  when projected in the up-down direction. 
     (2) Up and Down Movement of Drawer at Inside position 
     Then, as depicted in  FIG. 9 , the front cover  7  is further pivoted toward the exposing position and thus is located at the exposing position. 
     In response to the movement of the front cover  7  from the closing position to the exposing position, a tension is applied to the interlock portion  202  and thus the guide rails  185  are pulled frontward via the interlock portion  202 . Therefore, the link portions  184  pivot clockwise in left side view on the respective base shafts  123  and thus the guide rails  185  move upward and frontward. 
     At that time, the movement of the drawer  16  in the front-rear direction is restricted by the engagement of the projecting portion  97  of the stopper  90  with the engagement portion  186 . Therefore, the drawer  16  might not be able to move frontward but may move upward only inside the casing  2  in response to the forward movement of the guide rails  185 . 
     As described above, the drawer  16  is retained at the distant position at which the drawer  16  is located at a distance from the intermediate transfer belt  44 . 
     In response to the upward movement of the drawer  16 , the flange support portions  70  of the process cartridges  14  are separated from the respective positioning recesses  121  of the positioning plate  114 . 
     The left flanges  27  of the photosensitive drums  25  are also disengaged from the respective drum gears  124 . 
     (3) Pulling Out of Drawer 
     As indicated by the dashed line in  FIG. 3 , the stopper  90  of the drawer  16  is moved to the non-restricting position. In response to this, the projecting portion  97  is disengaged from the engagement portion  186 . 
     Then, as depicted in  FIG. 11 , the drawer  16  is pulled frontward through the opening  20 . 
     At that time, the drawer  16  moves frontward while the left thin-plate portion  93  of the bottom plate  85  is guided by the left first guide groove  188 , the lower surface of the left thin-plate portion  93  is guided by rotation of the rollers  190  of the left guide rail  185 , the right thin-plate portion  93  of the bottom plate  85  is guided by the first guide groove  188 , and the lower surface of the right thin-plate portion  93  is guided by rotation of the rollers  190  of the right guide rail  185 . 
     The rollers  89  of the drawer  16  are located within the second guide grooves  189 . The movement of drawer  16  is guided by rotation of the rollers  89 . 
     As described above, the drawer  16  is slid frontward and thus is retained at the outside position. 
     Thus, as indicated by a phantom line in  FIG. 11 , the process cartridges  14  are allowed to be detached from or attached to the drawer  16 . 
     7. Procedure for Installing Process Cartridges 
     In order to install a process cartridge  14  in the casing  2 , the detachment procedure is performed in a reverse order. 
     More specifically, as depicted in  FIG. 11 , the process cartridges  14  are placed on the support surfaces  94  of the recessed portions  88 , respectively. 
     Then, the drawer  16  having the process cartridges  14  attached is slid rearward to the distant position of the inside position through the opening  20 . 
     Thereafter, as depicted in  FIG. 3 , the stopper  90  of the drawer  16  is moved to the restricting position. Thus, as depicted in  FIG. 9 , the projecting portion  97  of the stopper  90  is engaged with the engagement portion  186 . 
     After that, the front cover  7  is pivoted from the exposing position toward the closing position. 
     In response to the movement of the front cover  7  from the exposing position toward the closing position, as depicted in  FIG. 7 , a tension applied to the interlock portion  202  decreases and thus the guide rails  185  move downward by their own weight. Therefore, the link portions  184  pivot counterclockwise in side view on the respective base shafts  123  and thus the guide rails  185  move rearward and downward. 
     At that time, the movement of the drawer  16  in the front-rear direction is restricted by the engagement of the projecting portion  97  of the stopper  90  with the engagement portion  186 . Thus, the drawer  16  might not be able to move further rearward within the casing  2  but may move downward only in response to the movement of the guide rails  185 . The drawer  16  is retained at the adjacent position of the inside position. 
     Therefore, the flange support portions  70  of the process cartridges  14  come into engagement with the respective positioning recesses  121  and thus the process cartridges  14  are positioned at their particular positions while the drums  26  are in contact with the outer surface of the upper portion of the intermediate transfer belt  44 . 
     Further, the left flanges  27  of the photosensitive drums  25  come into mesh with the respective drum gears  124 . 
     Then, as depicted in  FIGS. 5 and 6 , the front cover  7  is further pivoted to the closing position. Thus, the left protrusion  203  of the front cover  7  comes into contact with the front end of the translation cam  147  of the left movable member  133 , whereby the translation cam  147  moves rearward against an urging force of the spring  148 . The right protrusion  203  of the front cover  7  also comes into contact with the front end of the translation cam  147  of the right movable member  133 , whereby the translation cam  147  moves rearward against an urging force of the spring  148 . 
     In response to the rearward movement of the translation cam  147  of the left movable member  133 , the left movable member  133  is moved to the driving-force supply side first position, whereby the driving-force input members  130  are positioned at the engaged position. In response to the rearward movement of the translation cam  147  of the right movable member  133 , the right movable member  133  is moved the electric-power supply side first position, whereby the electric-power supply members  132  are positioned at the contacting position. 
     Thus, the installation of the process cartridges  14  into the casing  2  is completed. 
     8. Effects 
     (1) According to the above-described printer  1 , as depicted in  FIGS. 1 and 3 , the drawer  16  may be movable between the inside position and the outside position with respect to the casing  2  while the plate-like shaped bottom plate  85  having the support surfaces  94  supports the process cartridges  14 . 
     The plate-like shape of the bottom plate  85  may enable the driving-force input members  130  and the electric-power supply members  132  to be disposed adjacent to the respective process cartridges  14  as depicted in  FIGS. 2 and 6 . 
     Therefore, the configuration of the drawer  16  may be simplified and the size of the drawer  16  may be reduced as compared with a case where the drawer  16  has a generally box shape for accommodating the process cartridges  14  therein. 
     Accordingly, while the movement of the process cartridges  14  between the inside position and the outside position with respect to the casing  2  is achieved using such a drawer  16 , space saving may also be achieved inside the casing  2 , whereby reducing the printer  1  in size. 
     (2) According to the above-described printer  1 , as depicted in  FIG. 4 , the dimension in the up-down direction H 1  of the bottom plate  85  may be small relative to the dimension in the up-down direction H 2  of the process cartridge  14 . For example, the dimension in the up-down direction H 1  of the bottom plate  85  may be between 3% and 30% inclusive, preferably between 5% and 10% inclusive, of the dimension in the up-down direction H 2  of the process cartridge  14 . Therefore, the driving-force input members  130  and the electric-power supply members  132  may be surely disposed adjacent to the respective process cartridges  14 . 
     Accordingly, an appropriate layout may be ensured. 
     (3) According to the above-described printer  1 , as depicted in  FIG. 2 , the drawer  16  may be moved between the inside position and the outside position by which the left guide rail  185  and the right guide rail  185  guide the left thin-plate portion  93  and the right thin-plate portion  93 , respectively, of the bottom plate  85 . 
     Further, a driving force may be inputted to the driving-force receiving members  37  of the process cartridges  14  directly from the driving-force input members  130  and electric power may also be supplied to the electrode members  38  of the process cartridges  14  directly from the electric-power supply members  132  without using the drawer  16 . 
     Accordingly, space saving may be achieved inside the casing  2 , whereby reducing the printer  1  is size. 
     (4) According to the above-described printer  1 , as depicted in  FIG. 2 , the driving-force input members  130  are disposed higher than the drawer  16 . Therefore, a driving force may be easily inputted into the process cartridges  14  that are placed on the upper side of the drawer  16 . 
     Accordingly, an appropriate layout may be ensured. 
     (5) According to the above-described printer  1 , as depicted in  FIG. 10 , when the driving-force input members  130  are located at the disengaged position, the right end portion DE 2  of the body portion  136  of each of the driving-force input members  130  is located between the left guide rail  185  and the right guide rail  185  in the right-left direction. Therefore, the interval between a driving-force input member  130  and a corresponding driving-force receiving member  37  in the right-left direction may be shortened. 
     Accordingly, the driving-force input members  130  may be reduced in size in the right-left direction, and thus, an increase in size the casing  2  in the right-left direction may be restricted. 
     (6) According to the above-described printer  1 , as depicted in  FIGS. 6 and 8 , the driving-force input members  130  may be easily moved between the engaged position and the disengaged position by the left movable member  133 . 
     As depicted in  FIG. 2 , the left movable member  133  is disposed such that the left movable member  133  overlaps the left end portion of the bottom plate  85  when projected in the up-down direction. Therefore, an increase in size of the casing  2  in the right-left direction may be restricted. 
     (7) According to the above-described printer  1 , as depicted in  FIG. 10 , when the electric-power supply members  132  are located at the non-contacting position, the left end portion PE 2  of the body portion  142  of each of the electric-power supply members  132  is located between the left guide rail  185  and the right guide rail  185  in the right-left direction. Therefore, the interval between an electric-power supply member  132  and a corresponding electrode member  38  may be shortened. 
     Accordingly, the electric-power supply members  132  may be reduced in size in the right-left direction, and thus, an increase in size of the casing  2  in the right-left direction may be restricted. 
     (8) According to the above-described printer  1 , as depicted in  FIGS. 6 and 8 , the electric-power supply members  132  may be easily moved between the contacting position and the non-contacting position by the right movable member  133 . 
     As depicted in  FIG. 2 , the right movable member  133  is disposed such that the right movable member  133  overlaps the right end portion of the bottom plate  85  when projected in the up-down direction. Therefore, an increase in size of the casing  2  in the right-left direction may be restricted. 
     (9) According to the above-described printer  1 , as depicted in  FIGS. 2 and 6 , the left side plate  111  supports the driving-force input members  130  and the right side plate  111  supports the electric-power supply members  132 . Therefore, the printer  1  may have a simple configuration. 
     The process cartridges  14  supported by the drawer  16  may be allowed to move in the space defined by the side plates  111 . 
     Accordingly, further space saving may be achieved inside the casing  2 . 
     (10) According to the above-described printer  1 , as depicted in  FIGS. 2 and 6 , the power supply board  131  may be disposed between the right side plate  111  and the electric-power supply members  132  in the right-left direction. Therefore, an appropriate layout may be ensured. 
     (11) According to the above-described printer  1 , as depicted in  FIG. 4 , the dimension in the up-down direction H 1  of the bottom plate  85  is smaller than the dimension in the up-down direction H 4  of the driving-force receiving member  37 . Therefore, the drawer  16  may be further reduced in size. 
     (12) According to the above-described printer  1 , as depicted in  FIG. 4 , the dimension in the up-down direction H 3  of the recessed portion  88  may be 10% or less of the dimension in the up-down direction H 2  of the process cartridges  14 . Therefore, of the projected plane of the process cartridge  14  in the right-left direction when the drawer  16  supports the process cartridges  14 , the dimension in the up-down direction of the area of the portion that overlaps the bottom plate  85  may be surely 10% or less of the total area of the projected plane of the process cartridge  14 . 
     Accordingly, the drawer  16  may be reduced in size in the up-down direction. 
     (13) According to the above-described printer  1 , as depicted in  FIG. 1 , the intermediate transfer belt  44  is disposed below the drawer  16  and across the drawer  16  from the process cartridges  14 . A toner image may be transferred onto the intermediate transfer belt  44  disposed as described above 
     (14) According to the above-described printer  1 , as depicted in  FIGS. 1 and 3 , the photosensitive drums  25  are exposed through the respective openings  91  of the bottom plate  85 . Therefore, the photosensitive drums  25  and the intermediate transfer belt  44  may be easily come into contact with each other. 
     (15) According to the above-described printer  1 , as depicted in  FIGS. 1 and 3 , the movement of the drawer  16  in the front-rear direction may be restricted by the simple configuration in which the stopper  90  is engaged with the engagement portion  186  of the casing  2 . 
     (16) According to the above-described printer  1 , as depicted in  FIGS. 1 and 11 , the process cartridges  14  are supported by the drawer  16  as a set. 
     Accordingly, all of the process cartridges  14  may be moved together between the inside and the outside of the casing  2 . 
     9. Second Illustrative Embodiment 
     Referring to  FIG. 12 , a second illustrative embodiment will be described. An explanation will be given mainly for the parts different from the first illustrative embodiment, and an explanation will be omitted for the common parts by assigning the same or similar reference numerals thereto. 
     In the printer  1  of the first illustrative embodiment, as depicted in  FIG. 3 , a process cartridge  14  is supported only by a support surface  94  of a corresponding recessed portion  88 . 
     In a printer  1  of the second illustrative embodiment, as depicted in  FIG. 12 , a process cartridge  14  is supported by a corresponding support surface  94  while the process cartridge  14  receives a corresponding protrusion  206  through an engagement hole  207  defined in the process cartridge  14 . 
     More specifically, a bottom plate  85  further includes a plurality of, for example, four, protrusions  206  and process cartridges  14  each have an engagement hole  207 . All of the protrusions  206  have the same or similar configuration and all of the engagement holes  207  have the same or similar configuration. Therefore, one of the protrusions  206  and one of the engagement holes  207  will be described in detail. 
     A protrusion  206  restricts movement of a corresponding process cartridge  14  in the front-rear direction relative to the drawer  16 . The protrusion  206  is disposed at a substantially middle portion in the right-left direction of the recessed portion  88  in plan view and further to the rear than the opening  91 . The protrusion  206  protrudes upward from a bottom surface (e.g., the support surface  94 ) of the recessed portion  88 , and has a generally cylindrical column shape elongated in the right-left direction. An upper portion of the protrusion  206  is tapered toward the top such that a circumferential surface of the protrusion  206  is inclined toward its center in a diameter direction of the protrusion  206 . 
     An engagement hole  207  is defined in a substantially middle portion of the bottom wall  68  of the cartridge frame  64  of the process cartridge  14  in side view and penetrates the bottom wall  68  in the up-down direction. The engagement hole  207  has a generally oval shape elongated in the right-left direction in bottom view. 
     The bottom plate  85  supports a process cartridge  14  by the support surface  94  of one of the recessed portions  88  while the process cartridge  14  receives the protrusion  206  through the engagement hole  207  thereof. 
     According to the printer  1  of the second illustrative embodiment, as depicted in  FIG. 12 , the engagement of the protrusion  206  with the engagement hole  207  of the process cartridge  14  may restrict the movement of the process cartridge  14  relative to the drawer  16 . 
     Accordingly, even when the bottom plate  85  has a plate-like shape, the bottom plate  85  may support the process cartridges  14  with reliability. In particular, at the time of pulling the drawer  16  to the outside from the casing  2 , falling of the process cartridges  14  that may be caused due to the force of a pull of the drawer  16  may be prevented or reduced. 
     According to the second illustrative embodiment, the effect that is the same as the effect obtained in the first illustrative embodiment may be obtained. 
     10. Third Illustrative Embodiment 
     Referring to  FIG. 13 , a third illustrative embodiment will be described. An explanation will be given mainly for the parts different from the first illustrative embodiment, and an explanation will be omitted for the common parts by assigning the same or similar reference numerals thereto. 
     In the printer  1  of the first illustrative embodiment, as depicted in  FIG. 3 , a process cartridge  14  is supported only by a support surface  94  of a corresponding recessed portion  88 . 
     In a printer  1  of the third illustrative embodiment, as depicted in  FIG. 13 , a bottom plate  85  further includes a plurality of, for example, five, restricting portions  210 . All of the restricting portions  210  have the same or similar configuration, and therefore, one of the restricting portions  210  will be described in detail. 
     The restricting portion  210  regulates movement of a process cartridge  14  in the front-rear direction with respect to the drawer  16 . One of the restricting portions  210  is disposed at a front end portion of the bottom plate  85 , another of the restricting portions  210  is disposed at a rear end portion of the bottom plate  85 , and the remainder of the restricting portions  210  are disposed at respective different portions of the bottom plate  85  between the recessed portions  88 . 
     The restricting portion  210  protrudes upward from the upper surface  86  of the bottom plate  85 . The restricting portion  210  has a generally rectangular plate shape in plan view and has a thickness in the front-rear direction. A dimension in the up-down direction of the restricting portion  210  is approximately half of the dimension in the up-down direction of the process cartridge  14 . 
     A process cartridge  14  is supported by a support surface  94  of a corresponding recessed portion  88  while being sandwiched between corresponding two of the restricting portions  210  in the front-rear direction. 
     According to the printer  1  of the third illustrative embodiment, as depicted in  FIG. 13 , two of the restricting portions  210  sandwich a process cartridge  14  in the front-rear direction, whereby the movement of the process cartridge  14  with respect to the drawer  16  in the front-rear direction may be restricted. 
     Accordingly, even when the bottom plate  85  has a plate-like shape, the bottom plate  85  may support the process cartridges  14  with reliability. In particular, at the time of pulling the drawer  16  to the outside from the casing  2 , falling of the process cartridges  14  that may be caused due to the force of a pull of the drawer  16  may be prevented or reduced. 
     According to the third illustrative embodiment, the effect that is the same as the effect obtained in the first illustrative embodiment may be obtained. 
     11. Fourth Illustrative Embodiment 
     Referring to  FIG. 14 , a fourth illustrative embodiment will be described. An explanation will be given mainly for the parts different from the first illustrative embodiment, and an explanation will be omitted for the common parts by assigning the same or similar reference numerals thereto. 
     In the printer  1  of the first illustrative embodiment, as depicted in  FIGS. 2 and 3 , the process cartridges  14  are supported by the drawer  16  such that the lower end portions of the photosensitive drums  25  protrude downward relative to the bottom plate  85 . Therefore, when projected in the right-left direction, the bottom plate  85  overlaps the photosensitive drums  25 . 
     The drum gears  124  come into mesh with the gear teeth of the left flanges  27  of the photosensitive drums  25 , respectively, whereby a driving force from the power source (not depicted) is transmitted to the photosensitive drums  25 . 
     In a printer  1  of the fourth illustrative embodiment, as depicted in  FIG. 14 , a bottom plate  85  further includes a bent portion  213  at its left end portion. 
     The casing  2  further includes a plurality of, for example, four, driving-force input shafts  221 , instead of the drum gears  124  of the first illustrative embodiment. 
     The bent portion  213  includes a first portion  214  and a second portion  215 . 
     The first portion  214  has a generally plate shape extending in the front-rear direction. The first portion  214  extends downward and leftward from a left edge of the thick plate portion  92  of the bottom plate  85 . The first portion  214  has a plurality of, for example, four, cutaway portions  217 . 
     The cutaway portions  217  are spaced apart from each other in the front-rear direction while being arranged side by side in the front-rear direction. The cutaway portions  217  are recessed downward relative to an upper end of the first portion  214  and have a generally U shape in side view. Spacing between each cutaway portion  217  in the front-rear direction is the same as the spacing between each photosensitive drum  25  in the front-rear direction. 
     The second portion  215  has a generally plate shape extending in the front-rear direction. The second portion  215  extends leftward from a lower left end of the first portion  214 . The rollers  89  are disposed at a rear end portion of a left end of the second portion  215 . 
     The left flange  27  of each of the photosensitive drums  25  has not gear teeth on its peripheral surface but has a hole  219  defined therein. 
     The hole  219  is recessed rightward relative to a left surface of the left flange  27 . The hole  219  has a generally circular shape in side view. 
     All of the driving-force input shafts  221  have the same or similar configuration, and therefore, one of the driving-force input shafts  221  will be described in detail. A driving-force input shaft  221  is disposed inside the casing  2  such that the driving-force input shaft  221  is disposed to the left of a hole  219  of a corresponding photosensitive drum  25 . The driving-force input shaft  221  has a generally cylindrical column shape in the right-left direction. The driving-force input shaft  221  includes two engagement protrusions that protrude from a left end portion of the driving-force input shaft  221  in its diameter direction and have a generally cylindrical column shape. With this configuration, the driving-force input shaft  221  is configured to engage with the hole  219 . The driving-force input shaft  221  is capable of moving in the right-left direction. 
     In a state where a process cartridge  14  is supported by the drawer  16 , the flange support portion  70  of the photosensitive drum  25  of the process cartridge  14  is in engagement with one of the cutaway portions  217  and the hole  219  of the left flange  27  is exposed through the cutaway portion  217  when viewed from the left. 
     Then, the driving-force input shaft  221  moves rightward to come into engagement with the hole  219 , whereby a driving force from the power source (not depicted) is transmitted to the photosensitive drum  25 . 
     According to the fourth illustrative embodiment, a driving force may be inputted to the photosensitive drum  25  from the left of the process cartridge  14  while the drawer  16  may be reduced in size. 
     According to the fourth illustrative embodiment, the effect that is the same as the effect obtained in the first illustrative embodiment may be obtained. 
     12. Fifth Illustrative Embodiment 
     Referring to  FIG. 15 , a fifth illustrative embodiment will be described. An explanation will be given mainly for the parts different from the first illustrative embodiment, and an explanation will be omitted for the common parts by assigning the same or similar reference numerals thereto. 
     In the printer  1  according to the first illustrative embodiment, as depicted in  FIG. 1 , the exposing device  15 , the process cartridges  14 , the drawer  16 , the transfer unit  17  are arranged within the casing  2  in this order from above. Each of the process cartridges  14  includes the photosensitive drum  25  at its lower end portion. 
     In a printer  1  according to the fifth illustrative embodiment, as depicted in  FIG. 15 , a transfer unit  17 , process cartridges  14 , a drawer  16 , an exposing device  15  are arranged within a casing  2  in this order from above. Each of the process cartridges  14  includes a photosensitive drum  25  at its upper end portion. 
     The casing  2  further includes right and left movable arms  227  for pressing the process cartridges  14  upward. 
     The right and left movable arms  227  are spaced apart from each other in the right-left direction so as to sandwich the process cartridges  14  therebetween in the right-left direction. Both of the movable arms  227  have the same or similar configuration, and therefore, one of the movable arms  227  will be described in detail. A movable arm  227  has a generally rectangular column shape extending in the front-rear direction. The movable arm  227  includes a rotating shaft  228  and a plurality of, for example, four, urging members  229 . 
     The rotating shaft  228  has a generally cylindrical column shape. The rotating shaft  228  protrudes from a rear end portion of an outer surface of the movable arm  227  in the right-left direction toward the exterior of the printer  1 . Another end of the rotating shaft  228  in the right-left direction are fixed to the frame  112 . 
     The urging members  229  are disposed on an upper surface of the movable arm  227  while being spaced apart from each other in the front-rear direction. The urging members  229  protrude upward from the upper surface of the movable arm  227 . 
     The process cartridges  14  each have an engagement hole  231  and a laser-beam passage hole  232  in the bottom wall  68 . 
     The engagement hole  231  penetrates the bottom wall  68  in the up-down direction. The engagement hole  231  is defined in a substantially middle portion in the front-rear direction and in the right-left direction of the bottom wall  68 . The engagement hole  231  has a generally rectangular shape in bottom view. 
     The laser-beam passage hole  232  penetrates the bottom wall  68  in the up-down direction. The laser-beam passage hole  232  is defined in a particular portion further to the rear than the engagement hole  231 . The laser-beam passage hole  232  has a generally rectangular shape in bottom view and is elongated across the bottom wall  68  in the right-left direction. 
     Each recessed portion  88  of the bottom plate  85  further includes a laser-beam passage hole  234  and a restricting portion  235 . 
     The laser-beam passage hole  234  is configured to allow a laser beam emitted from the exposing device  15  to pass therethrough. The laser-beam passage hole  234  penetrates the bottom plate  85  in the up-down direction at a rear end portion of the recessed portion  88 . The laser-beam passage hole  234  has a generally rectangular shape in plan view and is elongated across the recessed portion  88  in the right-left direction. 
     The restricting portion  235  is configured to restrict movement of a process cartridge  14  in the front-rear direction relative to the drawer  16 . The restricting portion  235  is disposed at a substantially middle portion of the recessed portion  88  in plan view and further to the front than the laser-beam passage hole  234 . The restricting portion  235  has a generally rectangular column shape and protrudes upward from a bottom surface of the recessed portion  88 . 
     The process cartridges  14  are placed above the respective recessed portions  88  of the bottom plate  85 . More specifically, each of the process cartridges  14  is placed at a corresponding position while the process cartridge  14  receives the restricting portion  235  of the bottom plate  85  through the engagement hole  231  and the laser-beam passage hole  232  of the process cartridge  14  coincides with the laser-beam passage hole  234  of the bottom plate  85  in the up-down direction. 
     In a state where the right and left movable arms  227  extend frontward through their rotation on the rotating shaft  228 , the urging members  229  are into contact with the lower end portions of the flange support portions  70  of the respective process cartridges  14  to press the process cartridges  14  upward. 
     Thus, the photosensitive drums  25  are positioned such that the photosensitive drums  25  are in contact with the outer surface of the lower portion of the intermediate transfer belt  44  of the transfer unit  17 . 
     According to the printer  1  of the fifth illustrative embodiment, the exposing device  15  is disposed below the drawer  16  and the intermediate transfer belt  44  is disposed above the drawer  16 . In such a printer  1 , the exposing device  15  may expose the surfaces of the photosensitive drums  25  and a toner image may be transferred onto the intermediate transfer belt  44 . 
     While the exposing device  15  is disposed across the drawer  16  from the process cartridges  14 , the bottom plate  85  has the laser-beam passage holes  234 . With this configuration, the laser-beam passage holes  234  allow laser beams emitted from the exposing device  15  to pass therethrough and thus the surfaces of the photosensitive drums  25  may be exposed with the laser beams reliably. 
     According to the fifth illustrative embodiment, the effect that is the same as the effect obtained in the first illustrative embodiment may be obtained.