Patent Publication Number: US-11036180-B2

Title: Image forming apparatus with side frames

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/643,985, filed Jul. 7, 2017, which is a continuation of U.S. patent application Ser. No. 15/015,323 filed on Feb. 4, 2016, now U.S. Pat. No. 9,772,603 B2, issued Sep. 26, 2017, which claims priority from Japanese Patent Application No. 2015-022594, 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. 
     BACKGROUND 
     A known electrophotographic image forming apparatus includes a main body and one or more photosensitive drums. Each of the one or more photosensitive drums is disposed within the main body and is configured to carry a developing agent image thereon. 
     For example, a color laser printer includes a drum unit and four developing cartridges. The drum unit holds four photosensitive drums. The drum unit is attachable to and detachable from a casing of the color laser printer in a sliding manner. The developing cartridges are provided for the respective photosensitive drums and are attachable to and detachable from the drum unit. 
     In the color laser printer, the drum unit includes side plates that support respective end portions of the photosensitive drums in a width direction of the drum unit. The developing cartridges are attached to the drum unit while being interposed between the side plates in the width direction. 
     Each male coupling member is coupled to a female coupling member of a corresponding one of the developing cartridges through a coupling passing hole defined in one of the side plates. The coupled male coupling member is free from forward movement and backward movement relative to the corresponding female coupling member but is not rotatable relative to the corresponding female coupling member. With this coupling, a driving force is inputted to the female coupling members from the casing of the color laser printer. 
     SUMMARY 
     In the color laser printer, at the time of disengaging the coupling of the male coupling members and the female coupling members from each other, the male coupling members may need to be moved to respective positions closer to an exterior of the color laser printer than the side plate in the width direction of the drum unit so that the male coupling members do not interfere with the side plate when the drum unit is slid for detachment. 
     In order to achieve this, it may be necessary for the male coupling members to move at least by a distance of the thickness of the side plate. Nevertheless, this requirement may make it difficult to reduce a size of the color laser printer. 
     Accordingly, some embodiments of the disclosure provide for an image forming apparatus having a reduced size. 
    
    
     
       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. 
         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 support frame of  FIG. 1  in the first illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 4A  is a left side view depicting a process cartridge depicted in  FIG. 1  in the first illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 4B  is a right side view depicting the process cartridge depicted in  FIG. 1  in the first illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 5  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. 6  is a sectional view taken along line C-C of the printer of  FIG. 5  in the first illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 7  is a sectional view taken along line D-D of the printer of  FIG. 5  in the first illustrative embodiment according to one or more aspects of the disclosure, wherein the process cartridges are omitted for illustrating the support frame clearly. 
         FIG. 8A  is a front view depicting the support frame of  FIG. 7  in the first illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 8B  is a sectional view taken along line E-E of the support frame of  FIG. 7  in the first illustrative embodiment according to one or more aspects of the disclosure, wherein a switching member is located at a locking position and a lock member is located at a protruding position. 
         FIG. 8C  is a sectional view taken along line E-E of the support frame of  FIG. 7  in the first illustrative embodiment according to one or more aspects of the disclosure, wherein the switching member is located at an unlocking position and the lock member is located at a retracted position. 
         FIG. 9  is a sectional view taken along line C-C of the printer of  FIG. 5  in the first illustrative embodiment according to one or more aspects of the disclosure, wherein a front cover is slightly tilted from a closing position toward an exposing position, translation cams are located at respective pressing positions, main-body couplings are located at an engaged position, and main-body electrodes are located at a contacting position. 
         FIG. 10  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, wherein the front cover is located at the exposing position and the process cartridges are located at a second position. 
         FIG. 11  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, wherein the front cover is located at the exposing position and the process cartridge is located at the second position. 
         FIG. 12  is a sectional view depicting the printer in the first illustrative embodiment according to one or more aspects of the disclosure, wherein a process unit of  FIG. 1  is drawn from the main body. 
         FIG. 13A  is an upper front perspective view depicting a support frame in a variation of the first illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 13B  is a disassembled upper front perspective view depicting the support frame of  FIG. 13A  in the variation of the first illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 14  is a sectional view depicting a printer in a second illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 15  is a sectional view taken along line F-F of the printer of  FIG. 14  in the second illustrative embodiment according to one or more aspects of the disclosure. 
         FIG. 16  is a left side view depicting a process cartridge of  FIG. 14 . 
         FIG. 17  is a sectional view depicting the printer of  FIG. 14  in the second illustrative embodiment according to one or more aspects of the disclosure, wherein the front cover is located at the exposing position and the process cartridges are located at the second position. 
         FIG. 18  is a sectional view taken along line F-F of the printer of  FIG. 14  in the second illustrative embodiment according to one or more aspects of the disclosure, wherein the front cover is located at the exposing position and the process cartridge is located at the second position. 
     
    
    
     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. PRINTER 
     As depicted in  FIG. 1 , a printer  1  may be an intermediate transfer type color printer. 
     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 may be disposed in which it may be intended to be used as depicted in  FIG. 1 . 
     The printer  1  includes a main body  2 , a support frame  12 , a plurality of, for example, four, process cartridges  13 , a scanner unit  4 , a transfer unit  5 , and a fixing unit  6 . The main body  2  has an opening  7 . 
     The opening  7  is defined in a front end portion of the main body  2 . The opening  7  provides communication between the inside and the outside of the main body  2  in a front-rear direction (as an example of a sliding direction) to allow the support frame  12  and the process cartridges  13  to pass therethrough. 
     The main body  2  has a generally box shape. The main body  2  includes a front cover  8 , a feed tray  9 , and a discharge tray  11 . 
     The front cover  8  is disposed at a front end of the main body  2  so as to close the opening  7 . The front cover  8  has a general flat plate shape extending in an up-down direction. The front cover  8  is configured to swing between a closing position (e.g., a position of the front cover  8  depicted in  FIG. 1 ) and an exposing position (e.g., a position of the front cover  8  depicted in  FIG. 10 ) on its lower end. When the front cover  8  is located at the closing position (refer to  FIG. 1 ), the front cover  8  closes the opening  7 . When the front cover  8  is located at the exposing position (refer to  FIG. 10 ), the front cover  8  is inclined frontward relative to the closing position and exposes the opening  7 . 
     The feed tray  9  is disposed at a bottom portion of the main body  2 . The feed tray  9  is configured to support one or more sheets P therein. One or more sheets P supported by the feed tray  9  are fed, one by one, to between an intermediate transfer belt  29  and a secondary transfer roller  23  at a predetermined timing by rotation of rollers. 
     The discharge tray  11  is disposed at the top of the main body  2 . The discharge tray  11  is a recessed portion that is provided at the top of the main body  2  and recessed downward relative to an upper surface of the main body  2 . 
     The support frame  12  is disposed at a substantially middle portion of the main body  2  in the up-down direction. The support frame  12  has a generally frame-like shape extending in the front-rear direction. The support frame  12  supports a substantially middle portion of each of the process cartridges  13  in the up-down direction. 
     The process cartridges  13  are spaced apart from each other in the front-rear direction. All of the process cartridges  13  have the same or similar configuration except color of toner stored therein, and therefore, one of the process cartridges  13  will be described in detail. The process cartridge  13  includes a drum unit  14  and a developing unit  15 . 
     The drum unit  14  includes a photosensitive drum  16 , a charging roller  17 , and a drum cleaner  34 . 
     The photosensitive drum  16  is disposed at a lower end portion of the drum unit  14 . The photosensitive drum  16  is configured to rotate counterclockwise in left side view. 
     The charging roller  17  is disposed above and to the front of the photosensitive drum  16 . The charging roller  17  is in contact with an upper front end portion of the photosensitive drum  16 . The charging roller  17  is configured to charge a surface of the photosensitive drum  16 . 
     The drum cleaner  34  is disposed in front of the photosensitive drum  16 . The drum cleaner  34  is configured to clean the surface of the photosensitive drum  16 . 
     The developing unit  15  is disposed above and to the rear of the photosensitive drum  16 . The developing unit  15  includes a developing roller  18 , a supply roller  19 , a layer-thickness regulating blade  20 , and a toner storage portion  21 . 
     The developing roller  18  is disposed at a lower front end portion of the developing unit  15 . The developing roller  18  is in contact with a rear end portion of the photosensitive drum  16 . The developing roller  18  is configured to supply toner onto an electrostatic latent image held by the surface of the photosensitive drum  16  to develop the electrostatic latent image into a toner image. 
     The supply roller  19  is disposed behind the developing roller  18 . The supply roller  19  is in contact with a rear end portion of the developing roller  18 . The supply roller  19  is configured to supply toner stored in the toner storage portion  21  onto the developing roller  18 . 
     The layer-thickness regulating blade  20  is disposed above and to the rear the developing roller  18 . The layer-thickness regulating blade  20  is in contact with an upper rear end portion of the developing roller  18 . The layer-thickness regulating blade  20  is configured to regulate a thickness of a toner layer held by the developing roller  18 . 
     The toner storage portion  21  is disposed above the supply roller  19  and the layer-thickness regulating blade  20 . The toner storage portion  21  is configured to store toner therein. 
     The scanner unit  4  is disposed in an upper end portion of the main body  2  and above the process cartridges  13 . The scanner unit  4  is configured to expose the surface of each of the photosensitive drums  16  charged by the respective charging rollers  17  to form an electrostatic latent image on the surface of each of the photosensitive drums  16  based on image data. 
     The transfer unit  5  includes a belt unit  22 , the secondary transfer roller  23 , a belt cleaner  24 , and a waste toner storage  33 . 
     The belt unit  22  is disposed below the process cartridges  13 . The belt unit  22  includes the intermediate transfer belt  29 , and a plurality of, for example, four, primary transfer rollers  28 . 
     The intermediate transfer belt  29  may be an endless belt. The intermediate transfer belt  29  rotates clockwise in left side view while being in contact with all of the photosensitive drums  16 . 
     The primary transfer rollers  28  are disposed below the respective photosensitive drums  16  while sandwiching the intermediate transfer belt  29  therebetween. The primary transfer rollers  28  are configured to transfer toner images onto an outer surface of the intermediate transfer belt  29  from the surfaces of the respective photosensitive drums  16 . 
     The secondary transfer roller  23  is disposed behind the belt unit  22  and is in contact with the intermediate transfer belt  29 . The secondary transfer roller  23  is configured to transfer the toner images onto a sheet P from the outer surface of the intermediate transfer belt  29 . 
     The belt cleaner  24  is disposed above a rear end portion of the belt unit  22 . The belt cleaner  24  is configured to clean the outer surface of the intermediate transfer belt  29 . 
     The waste toner storage  33  is disposed in a lower end portion of the main body  2 . The waste toner storage  33  has a generally box shape. The waste toner storage  33  is connected with the belt cleaner  24  by a predetermined piping arrangement. The waste toner storage  33  is configured to store therein transfer residual toner and paper dust collected by the belt cleaner  24 . 
     The fixing unit  6  is disposed above the secondary transfer roller  23 . The fixing unit  6  includes a heat roller  6 A and a pressing roller  6 B. The pressing roller  6 B is in pressure contact with a rear end portion of the heat roller  6 A. The heat roller  6 A and the pressing roller  6 B are configured to fix the toner images onto a sheet P by heat. 
     2. DETAILS OF PROCESS UNIT 
     (1) Support Frame 
     As depicted in  FIGS. 3 and 7 , the support frame  12  has a generally rectangular frame shape in plan view. The support frame  12  is configured to move between an inside position (e.g., a position of the support frame  12  depicted in  FIG. 1 ) and an outside position (e.g., a position of the support frame  12  depicted in  FIG. 12 ) in the front-rear direction (e.g., in the sliding direction) through the opening  7 . When the support frame  12  is located at the inside position (refer to  FIG. 1 ), the support frame  12  is positioned inside the main body  2 . When the support frame  12  is located at the outside position (refer to  FIG. 12 ), the support frame  12  is positioned outside the main body  2 . The support frame  12  includes a first side frame  41 L, a second side frame  41 R, a plurality of, for example, five, beam members  42 , a front beam  43 , a lock member  57 , and a switching member  58 . 
     (a) Side Frames 
     The first side frame  41 L defines a left end of the support frame  12 . The first side frame  41 L has a bar shape extending in the front-rear direction, and more specifically, has a rectangular column shape. The first side frame  41 L may be made of a hard resin material. A dimension in the up-down direction L 1  and a dimension in the right-left direction L 2  of the first side frame  41 L are smaller than a dimension in the front-rear direction L 3  of the first side frame  41 L. The dimension in the up-down direction L 1  of the first side frame  41 L is smaller than the dimension in the right-left direction L 2  of the first side frame  41 L. The first side frame  41 L includes a first guided portion  41 A, a first cartridge-support portion  41 B, and a roller  44 . The first guided portion  41 A is guided by a first guide portion  65 L when the support frame  12  moves in the sliding direction. The first cartridge-support portion  41 B is configured to support the process cartridges  13 . The first side frame  41 L further has a plurality of, for example, five, engagement holes  45 . 
     The first guided portion  41 A constitutes a left half portion of the first side frame  41 L and is engaged in a first guide groove  65 A of the first guide portion  65 L. 
     The first cartridge-support portion  41 B constitutes a right half portion of the first side frame  41 L and is disposed further to the right than the first guide groove  65 A of the first guide portion  65 L. 
     The roller  44  of the first side frame  41 L is rotatably supported by a rear end portion of a left surface of the first side frame  41 L. The roller  44  has a generally circular plate shape having a thickness in the right-left direction. The roller  44  is engaged in a second guide groove  65 B of the first guide portion  65 L. 
     The engagement holes  45  of the first side frame  41 L are defined over an area from a front end portion to a rear end portion of the first side frame  41 L while being spaced apart from each other in the front-rear direction. The engagement holes  45  are recessed leftward relative to a right surface of the first side frame  41 L. The engagement holes  45  have a generally rectangular shape in side view. 
     The second side frame  41 R defines a right end of the support frame  12 . The second side frame  41 R is disposed at the same level as the first side frame  41 L in the up-down direction. The second side frame  41 R has a configuration similar to the first side frame  41 L. More specifically, the second side frame  41 R has a bar shape extending in the front-rear direction, and more specifically, has a rectangular column shape. The second side frame  41 R may be made of a hard resin material. A dimension in the up-down direction L 1  and a dimension in the right-left direction L 2  of the second side frame  41 R are smaller than a dimension in the front-rear direction L 3  of the second side frame  41 R. The dimension in the up-down direction L 1  of the second side frame  41 R is smaller than the dimension in the right-left direction L 2  of the second side frame  41 R. The second side frame  41 R includes a second guided portion  41 C, a second cartridge-support portion  41 D, and a roller  44 . The second guided portion  41 C is guided by a second guide portion  65 R when the support frame  12  moves in the sliding direction. The second cartridge-support portion  41 D is configured to support the process cartridges  13 . The second side frame  41 R further has a plurality of, for example, five, engagement holes  45 . 
     The second guided portion  41 C constitutes a right half portion of the second side frame  41 R and is engaged in a first guide groove  65 A of the second guide portion  65 R. 
     The second cartridge-support portion  41 D constitutes a left half portion of the second side frame  41 R and is disposed further to the left than the first guide groove  65 A of the second guide portion  65 R. 
     The roller  44  of the second side frame  41 R is rotatably supported by a rear end portion of a right surface of the second side frame  41 R. The roller  44  has a generally circular plate shape having a thickness in the right-left direction. The roller  44  is engaged in a second guide groove  65 B of the second guide portion  65 R. 
     The engagement holes  45  of the second side frame  41 R are defined over an area from a front end portion to a rear end portion of the second side frame  41 R spaced apart from each other in the front-rear direction. The engagement holes  45  are recessed rightward relative to a left surface of the second side frame  41 R. The engagement holes  45  have a generally rectangular shape in side view. 
     (b) Beam Members 
     The beam members  42  are disposed between the first side frame  41 L and the second side frame  41 R in the right-left direction while being spaced apart from each other in the front-rear direction at regular intervals. The beam members  42  have a generally bar shape extending in the right-left direction, and more specifically, have a generally rectangular column shape. The beam members  42  may be made of metallic material having a higher stiffness, for example, stainless. A dimension in the up-down direction L 6  of the beam member  42  is smaller than the dimension in the up-down direction L 1  of the first side frame  41 L and the dimension in the up-down direction L 1  of the second side frame  41 R. A right end portion of each of the beam members  42  is fitted in a corresponding one of the engagement holes  45  of the second side frame  41 R. A left end portion of each of the beam members  42  is fitted in a corresponding one of the engagement holes  45  of the first side frame  41 L. Thus, a space between the first side frame  41 L and the second side frame  41 R is divided into four areas in the front-rear direction by the beam members  42 . In other words, four openings  12 A are defined between the first side frame  41 L and the second side frame  41 R. 
     (c) Front Beam 
     The front beam  43  is disposed in front of the frontmost beam member  42  and between a front end portion of the first side frame  41 L and a front end portion of the second side frame  41 R in the right-left direction. The front beam  43  has a generally rectangular column shape extending in the right-left direction. The front beam  43  may be made of a hard resin material. A left end portion of the front beam  43  is contiguous with the front end portion of the first side frame  41 L. A right end portion of the front beam  43  is contiguous with the second side frame  41 R. As depicted in  FIGS. 7 and 8A , the front beam  43  includes an accommodating portion  43 A for accommodating the switching member  58  therein and an accommodating portion  43 B for accommodating the lock member  57  therein. 
     The accommodating portion  43 A is disposed at a substantially middle portion of the front beam  43  in the right-left direction. The accommodating portion  43 A has a generally cylindrical shape. The accommodating portion  43 A extends in the front-rear direction and has a closed rear end. A dimension in a diameter direction L 7  of the accommodating portion  43 A is greater than the dimension in the up-down direction L 1  of the first side frame  41 L and the dimension in the up-down direction L 1  of the second side frame  41 R. 
     The accommodating portion  43 B is disposed at a left portion of the front beam  43 . The accommodating portion  43 B may be a through hole extending in the right-left direction. A right end of the accommodating portion  43 B is contiguous with the accommodating portion  43 A such that the inside of the accommodating portion  43 B is in communication with the inside of the accommodating portion  43 A. The accommodating portion  43 B passes through the first side frame  41 L and a left end of the accommodating portion  43 B is exposed through the left surface of the support frame  12 . 
     (d) Lock Member 
     The lock member  57  is disposed inside the accommodating portion  43 B. The lock member  57  has a generally cylindrical shape extending in the right-left direction. The lock member  57  is movable in the right-left direction between a protruding position (e.g., a position of the lock member  57  depicted in  FIG. 8B ) and a retracted position (e.g., a position of the lock member  57  depicted in  FIG. 8C ). When the lock member  57  is located at the protruding position (refer to  FIG. 8B ), a left end portion of the lock member  57  protrudes relative to the left surface of the first side frame  41 L. When the lock member  57  is located at the retracted position (refer to  FIG. 8C ), an entire portion of the lock member  57  is retracted within the accommodating portion  43 B, that is the left end portion of the lock member  57  does not protrudes relative to the left surface of the first side frame  41 L. The lock member  57  is urged rightward toward the retracted position at all times by a compression spring  59 . When the lock member  57  is located at the retracted position, a right end portion of the lock member  57  is located inside the accommodating portion  43 A. When the lock member  57  is located at the protruding position, the right end portion of the lock member  57  is located at a position further to the left than the right end portion of the lock member  57  that is located at the retracted position and thus is not positioned inside the accommodating portion  43 A. 
     (e) Switching Member 
     The switching member  58  is disposed inside the accommodating portion  43 A. The switching member  58  has a generally circular plate shape having a thickness in the front-rear direction. The switching member  58  is rotatable between a locking position (e.g., a position of the switching member  58  depicted in  FIG. 8B ) and an unlocking position (e.g., a position of the switching member  58  depicted in  FIG. 8C ). When the switching member  58  is located at the locking position (refer to  FIG. 8B ), the switching member  58  retains the lock member  57  at the protruding position. When the switching member  58  is located at the unlocking position (refer to  FIG. 8C ), the switching member  58  retains the lock member  57  at the retracted position. The switching member  58  has a groove  58 A. 
     The groove  58 A is located at an upper left position in the switching member  58  when the switching member  58  is located at the unlocking position (refer to  FIG. 8C ). The groove  58 A is recessed relative to a peripheral surface of the switching member  58  in a diameter direction of the switching member  58  and extends approximately 90 degrees around the switching member  58  along a circumferential direction of the switching member  58 . A depth of the groove  58 A becomes shallower in a clockwise direction in front view. The depth at a most upstream end of the groove  58 A is substantially equal to a protruding amount of the right end portion of the lock member  57  that protrudes inside the accommodating portion  43 A in the right-left direction when the lock member  57  is located at the retracted position. 
     (2) Process Cartridges 
     As described above, all of the process cartridges  13  have the same or similar configuration except color of toner stored therein and therefore, one of the process cartridges  13  will be described in detail. As depicted in  FIGS. 2 and 5 , the process cartridge  13  has a generally rectangular column shape extending in the right-left direction. Through insertion of the process cartridge  13  in the up-down direction in an appropriate one of the openings  12 A of the support frame  12 , the process cartridge  13  is placed in the appropriate opening  12 A of the support frame  12  such that the photosensitive drum  16  of the process cartridge  13  is positioned below the support frame  12 . 
     That is, the process cartridge  13  is disposed between corresponding adjacent two of the beam members  42  in the front-rear direction while being disposed between the first side frame  41 L and the second side frame  41 R in the right-left direction. When viewed in the right-left direction, the process cartridge  13  includes a lower portion  13 A and an upper portion  13 B with respect to the support frame  12 . The lower portion  13 A is located below the support frame  12  and the upper portion  13 B is located above the support frame  12 . The lower portion  13 A and the upper portion  13 B are exposed from the support frame  12 . Of a projected plane A 1  of the process cartridge  13 , an area of each portion A 2  that overlaps one of the first side frame  41 L and the second side frame  41 R may be 30% or less of a total area of the projected plane A 1 . 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 side frames and other structures. 
     A dimension in the up-down direction L 4  of the process cartridge  13  is greater than the dimension in the up-down direction L 1  of the first side frame  41 L and the dimension in the up-down direction L 1  of the second side frame  41 R. In other words, the dimension in the up-down direction L 1  of the first side frame  41 L and the dimension in the up-down direction L 1  of the second side frame  41 R are smaller than the dimension in the up-down direction L 4  of the process cartridge  13 . More specifically, the dimension in the up-down direction L 1  of the first side frame  41 L and the dimension in the up-down direction L 1  of the second side frame  41 R may be between 5% and 30% inclusive, and preferably, between 10% and 20% inclusive, of the dimension in the up-down direction L 4  of the process cartridge  13 . 
     The process cartridge  13  is movable between a first position (e.g., a position of the process cartridge  13  depicted in  FIG. 2 ) and a second position (e.g., a position of the process cartridge depicted in  FIG. 11 ). When the process cartridge  13  is located at the first position (refer to  FIG. 2 ), the photosensitive drum  16  is in contact with the intermediate transfer belt  29 . When the process cartridge  13  is located at the second position (refer to  FIG. 11 ), the photosensitive drum  16  is positioned at a distance from the intermediate transfer belt  29 . 
     As described above, the process cartridge  13  includes the drum unit  14  and the developing unit  15 . 
     (a) Drum Unit 
     As depicted in  FIGS. 2 and 6 , the drum unit  14  has a generally box shape with its upper end opened. The drum unit  14  includes a first side wall  46 L, a second side wall  46 R, a front wall  47 , and a rear wall  48 . 
     (a-1) Side Walls 
     As depicted in  FIGS. 2 and 4A , the first side wall  46 L defines a left end of the drum unit  14 . The first side wall  46 L has a generally rectangular flat plate shape in side view. The first side wall  46 L includes a drum support portion  49 , an urging portion  50 , and a developing-unit support portion  51 . 
     The drum support portion  49  is disposed to the front with respect to a middle portion of the first side wall  47  in the front-rear direction at a lower end portion of the first side wall  46 L. The drum support portion  49  has a generally cylindrical shape extending in the right-left direction. The drum support portion  49  penetrates the first side wall  46 L in the right-left direction. 
     The urging portion  50  is disposed at a substantially middle portion of the first side wall  46 L in the up-down direction. The urging portion  50  includes an accommodating member  40 , a contact member  53 , and a plurality of, for example, two, compression springs  54 . 
     The accommodating member  40  protrudes leftward from a left surface of the first side wall  46 L and has a generally box shape extending in the front-rear direction. The accommodating member  40  overlaps the first side frame  41 L when projected in the up-down direction. The accommodating member  40  has an opening  40 A. 
     The opening  40 A penetrates a portion of a lower wall of the accommodating member  40  in the up-down direction. The opening  40 A extends across almost an entire portion of the lower wall of the accommodating member  40  in the front-rear direction other than front and rear end portions of the accommodating member  40  in the front-rear direction. 
     The contact member  53  is placed in the opening  40 A of the accommodating member  40 . The contact member  53  extends in the front-rear direction and has a generally box shape with its upper end opened. The contact member  53  is in contact with an upper surface of the first cartridge-support portion  41 B of the first side frame  41 L. The contact member  53  is movable between a retracted position (e.g., a position of the contact member  53  depicted  FIG. 5 ) and a protruding position (e.g., a position of the contact member  53  depicted  FIG. 10 ). When the contact member  53  is located at the retracted position (refer to  FIG. 5 ), the contact member  53  is positioned within the accommodating member  40  via the opening  40 A while contracting the compression springs  54 . When the contact member  53  is located at the protruding position (refer to  FIG. 10 ), the contact member  53  protrudes relative to the accommodating member  40  via the opening  40 A so as to release the compression of the compression springs  54 . The contact member  53  includes a plurality of, for example, two, engagement portions  53 A. 
     The engagement portions  53 A are spaced apart from each other in the front-rear direction. One of the engagement portions  53 A (e.g., the front engagement portion  53 A) has a generally flat plate shape and protrudes frontward from a front end of the contact member  53 . The front engagement portion  53 A is in engagement with a lower wall of the accommodating member  40  at a circumference edge of the opening  40 A. The other of the engagement portions  53 A (e.g., the rear engagement portion  53 A) also has a generally flat plate shape and protrudes rearward from a rear end of the contact member  53 . The rear engagement portion  53 A is in engagement with the lower wall of the accommodating member  40  at the circumference edge of the opening  40 A. 
     The compression springs  54  are disposed in a contracted state while being spaced apart from each other in the front-rear direction inside the urging portion  50 . The compression springs  54  are coil springs that extends and contracts in the up-down direction. In each of the compression springs  54 , an upper end of the compression spring  54  is in contact with an inner surface, e.g., a lower surface, of an upper wall of the accommodating member  40  and a lower end of the compression spring  54  is in contact with an inner surface, e.g., an upper surface, of the lower wall of the accommodating member  40 . Thus, the compression springs  54  urges the contact member  53  downward with respect to the accommodating member  40 . In other words, the compression springs  54  urge the accommodating member  40  upward with respect to the contact member  53 . That is, the compression springs  54  urge the accommodating member  40  upward at front and rear end portions of the accommodating member  40  in the front-rear direction. 
     The developing-unit support portion  51  is disposed at a substantially middle portion of an upper end portion of the first side wall  46 L in the front-rear direction. The developing-unit support portion  51  has a generally circular shape in side view and penetrates the first side wall  46 L in the right-left direction. 
     As depicted in  FIGS. 2 and 4B , the second side wall  46 R defines a right end of the drum unit  14 . The second side wall  46 R has a generally rectangular flat plate shape in side view. The second side wall  46 R includes a drum support portion  49 , an urging portion  50 , a developing-unit support portion  51 , and an opening  52 . That is, the second side wall  46 R has a configuration similar to the first side wall  46 L except further has an opening  52 . The accommodating member  40  of the second side wall  46 R protrudes rightward from a right surface of the second side wall  46 R. The accommodating member  40  overlaps the second side frame  41 R when projected in the up-down direction. The contact member  53  of the second side wall  46 R is in contact with an upper surface of the second cartridge-support portion  41 D of the second side frame  41 R. 
     The opening  52  is defined in a lower end portion of the second side wall  46 R and is disposed behind the drum support portion  49  in the front-rear direction. The opening  52  penetrates the second side wall  46 R in the right-left direction. The opening  52  has an arc shape in side view, in which the developing-unit support portion  51  may be the center of the arc. The opening  52  extends upward toward the rear. 
     (a-2) Front Wall 
     As depicted in  FIGS. 1 and 6 , the front wall  47  is disposed between a front end portion of the first side wall  46 L and a front end portion of the second side wall  46 R. The front wall  47  has a generally flat plate shape extending in the right-left direction. The front wall  47  also serves as a front wall of the drum cleaner  34 . A left end of the front wall  47  is connected with the front end portion of the first side wall  46 L. A right end of the front wall  47  is connected with the front end portion of the second side wall  46 R. The front wall  47  includes a rib  47 A (refer to  FIGS. 4A and 4B ). 
     The rib  47 A is disposed at a substantially middle portion of the front wall  47  in the up-down direction. The rib  47 A protrudes frontward from a front surface of the front wall  47 . The rib  47 A has a generally flat plate shape extending in the right-left direction. The rib  47 A is in contact with an upper surface of a rear end portion of a corresponding beam member  42 . 
     (a-3) Rear Wall 
     The rear wall  48  is disposed between a rear end portion of the first side wall  46 L and a rear end portion of the second side wall  46 R. The rear wall  48  has a generally flat plate shape extending in the right-left direction. A left end of the rear wall  48  is connected with the rear end portion of the first side wall  46 L. A right end portion of the rear wall  48  is connected with the rear end portion of the second side wall  46 R. The rear wall  48  includes a rib  48 A (refer to  FIGS. 4A and 4B ). 
     The rib  48 A is disposed at a substantially middle portion of the rear wall  48  in the up-down direction. The rib  48 A protrudes rearward from a rear surface of the rear wall  48 . The rib  48 A has a generally flat plate shape extending in the right-left direction. The rib  48 A is in contact with an upper surface of a front end portion of a corresponding beam member  42 . 
     (a-4) Photosensitive Drum 
     As depicted in  FIGS. 2 and 4A , the photosensitive drum  16  includes a drum body  16 A, a first flange member  16 B, and a second flange member  16 E. 
     The drum body  16 A has a generally cylindrical shape extending in the right-left direction. The drum body  16 A has a photosensitive layer on its surface. 
     The first flange member  16 B is rotatably fitted to the drum support portion  49  of the first side wall  46 L while being attached to a left end portion of the drum body  16 A so as not to be rotatable relative to the drum body  16 A. The first flange member  16 B has a generally cylindrical column shape extending in the right-left direction. The first flange member  16 B has a coupling recess  16 C and includes a plurality of, for example, two protrusions  16 D. The first flange member  16 B is configured to engage with a main-body coupling  70  of the main body  2  and receive a driving force from the main body  2 . 
     The coupling recess  16 C is recessed rightward relative to a left surface of the first flange member  16 B. The coupling recess  16 C has a generally circular shape in side view. A dimension in a diameter direction L 5  of the coupling recess  16 C of the photosensitive drum  16  (refer to  FIG. 5 ) is greater than the dimension in the up-down direction L 1  of the first side frame  41 L. 
     The protrusions  16 D are spaced apart from each other in the diameter direction of the coupling recess  16 C in the coupling recess  16 C while facing each other. The protrusions  16 D protrude toward the center of the coupling recess  16 C in the diameter direction from an inner circumferential surface of the coupling recess  16 C. The protrusions  16 D each have a generally rectangular shape in side view. 
     The second flange member  16 E is rotatably fitted to the drum support portion  49  of the second side wall  46 R while being attached to a right end portion of the drum body  16 A so as not to be rotatable relative to the drum body  16 A. The second flange member  16 E has a generally cylindrical column shape extending in the right-left direction. That is, the second flange member  16 E has a configuration similar to the first flange member  16 B. The second flange member  16 E does not include a coupling recess  16 C and protrusions  16 D that the first flange member  16 B includes. 
     (b) Developing Unit 
     As depicted in  FIGS. 2 and 6 , the developing unit  15  includes a developing frame  55  and a developing electrode  56 . The developing electrode  56  is configured to receive electric power from the main body  2 . 
     The developing frame  55  has a generally box shape extending in the right-left direction. The developing frame  55  includes a toner storage portion  21  inside thereof (refer to  FIG. 1 ). As depicted above, the developing frame  55  includes the developing roller  18 , the supply roller  19 , and the layer-thickness regulating blade  20 . The developing frame  55  further includes a first swing shaft  55 A and a second swing shaft  55 B. 
     The first swing shaft  55 A is disposed at an upper portion of a left end of the developing frame  55 . The first swing shaft  55 A has a generally cylindrical shape and extends leftward from a left surface of the developing frame  55 . The second swing shaft  55 B is disposed at an upper portion of a right end of the developing frame  55 . The second swing shaft  55 B has a generally cylindrical shape and extends rightward from a right surface of the developing frame  55 . The first swing shaft  55 A and the second swing shaft  55 B have a common axis as their center. The first swing shaft  55 A is rotatably fitted to the developing-unit support portion  51  of the first side wall  46 L. The second swing shaft  55 B is rotatably fitted to the developing-unit support portion  51  of the second side wall  46 R. The developing unit  15  is swingable on the first swing shaft  55 A and the second swing shaft  55 B between a contacting position (e.g., a position of the developing unit  15  depicted in  FIG. 1 ) and a non-contacting position (not depicted). When the developing unit  15  is located at the contacting position (refer to  FIG. 1 ), the developing roller  18  is in contact with the photosensitive drum  16 . When the developing unit  15  is located at the non-contacting position (not depicted), the developing roller  18  is positioned at a distance from the photosensitive drum  16 . 
     As depicted in  FIGS. 4B and 6 , the developing electrode  56  is supported by a right end of the developing frame  55  such that the developing electrode  56  is exposed through the opening  52  of the second side wall  46 R when viewed from the right. The developing electrode  56  has a generally oval shape in side view and is elongated in the front-rear direction. The developing electrode  56  is electrically connected to the developing roller  18  and the supply roller  19 . 
     3. DETAILS OF MAIN BODY 
     As depicted in  FIGS. 1 and 2 , the main body  2  further includes an outer frame  61 , an inner frame  62 , a driving unit  63 , an electric supply unit  64 , a first guide portion  65 L, a second guide portion  65 R, a first pressing portion  60 L, and a second pressing portion  60 R. 
     (1) Outer Frame and Inner Frame 
     The outer frame  61  constitutes an exterior of the main body  2 . The outer frame  61  has a generally box shape. The outer frame  61  may be made of a hard resin. The outer frame  61  includes the discharge tray  11 . 
     The inner frame  62  is disposed inside the outer frame  61 . The inner frame  62  has a generally rectangular cylindrical shape. The inner frame  62  extends in the front-rear direction and has an open front end and an open rear end. The inner frame  62  includes a first side plate  66 L, a second side plate  66 R, an upper plate  67 , a lower plate  68 , a first positioning plate  69 L, and a second positioning plate  69 R. The first side plate  66 L supports the main-body couplings  70 . The second side plate  66 R supports main-body electrodes  77 . 
     As depicted in  FIGS. 2 and 6 , the first side plate  66 L is disposed to the right of a left wall of the outer frame  61  and spaced apart from the left wall of the outer frame  61 . The first side plate  66 L has a generally flat plate shape extending in the up-down direction. The first side plate  66 L may be made of a metal having a higher stiffness, for example, stainless or plated iron. The first side plate  66 L has a plurality of, for example, four, holes  66 A. 
     The holes  66 A are defined in a substantially middle portion of the first side plate  66 L in the up-down direction so as to face the respective photosensitive drums  16  from left. That is, the holes  66 A are spaced apart from each other in the front-rear direction. The holes  66 A penetrate the first side plate  66 L in the right-left direction. 
     The second side plate  66 R is disposed to the left of a right wall of the outer frame  61  and spaced apart from the right wall of the outer frame  61 . The second side plate  66 R has a generally flat plate shape in the up-down direction. The second side plate  66 R may be made of a metal having a higher stiffness, for example, stainless or plated iron. 
     As depicted in  FIG. 2 , the upper plate  67  is disposed at an upper end portion of the inner frame  62 . The upper plate  67  has a generally flat plate shape in the right-left direction. The upper plate  67  may be made of a metal, for example, stainless or plated iron. The upper plate  67  extends between an upper end portion of the first side plate  66 L and an upper end portion of the second side plate  66 R. The upper plate  67  supports the scanner unit  4 . 
     The lower plate  68  is disposed at a lower end portion of the inner frame  62 . The lower plate  68  has a generally flat plate shape extending in the right-left direction. The lower plate  68  may be made of a metal, for example, stainless and plated iron. The lower plate  68  is disposed above the feed tray  9  and extends between a lower end portion of the first side plate  66 L and a lower end portion of the second side plate  66 R. 
     As depicted in  FIGS. 2 and 5 , the first positioning plate  69 L and the second positioning plate  69 R are disposed between the first side plate  66 L and the second side plate  66 R at a lower end portion of the inner frame  62  while being spaced apart from each other in the right-left direction. The first positioning plate  69 L and the second positioning plate  69 R have a generally flat plate shape extending in the up-down direction. The first positioning plate  69 L and the second positioning plate  69 R may be made of a metal, for example, stainless or plated iron and have an identical shape. A lower end of the first positioning plate  69 L and a lower end of the second positioning plate  69 R are joined to an upper surface of the lower plate  68 . The first positioning plate  69 L has a plurality of, for example, four, positioning recesses  69 A. The second positioning plate  69 R also has a plurality of, for example, four, positioning recesses  69 A. 
     The positioning recesses  69 A of the first positioning plate  69 L are defined in an upper end portion of the first positioning plate  69 L while being spaced apart from each other at regular intervals in the front-rear direction. The positioning recesses  69 A of the first positioning plate  69 L are recessed downward relative to an upper end of the first positioning plate  69 L. The positioning recesses  69 A of the second positioning plate  69 R are defined in an upper end portion of the second positioning plate  69 R while being spaced apart from each other at regular intervals in the front-rear direction. The positioning recesses  69 A of the second positioning plate  69 R are recessed downward relative to an upper end of the second positioning plate  69 R. The positioning recesses  69 A of the first positioning plate  69 L and the second positioning plate  69 R have a generally U shape in side view with its upper end opened. Each of the positioning recesses  69 A receives the drum support portion  49  of a corresponding process cartridge  13  to position the photosensitive drum  16  of the corresponding process cartridge  14  in the front-rear direction. 
     (2) Driving Unit 
     As depicted in  FIGS. 2 and 6 , the driving unit  63  is supported by a substantially middle portion of the first side plate  66 L in the up-down direction. The driving unit  63  includes a frame  85 , a plurality of, for example, four, drum drive gears  71 , a translation cam  72 , a plurality of, for example, four, main-body couplings  70 , and a plurality of, for example, four, compression springs  88 . 
     (a) Frame 
     The frame  85  is disposed to the right of the first side plate  66 L. The frame  85  has a generally box shape extending in the front-rear direction. The frame  85  has a plurality of, for example, four, holes  85 A and a hole  85 B. The main-body couplings  70  pass through the respective holes  85 A. The translation cam  72  passes through the hole  85 B. 
     The holes  85 A are defined in an upper end portion of a right wall of the frame  85 . The holes  85 A are spaced apart from each other in the front-rear direction while facing the respective photosensitive drums  16  from left. The holes  85 A penetrate the right wall of the frame  85  in the right-left direction. 
     The hole  85 B is defined in a right end portion of a front wall of the frame  85 . The hole  85 B penetrates the front wall of the frame  85  in the front-rear direction. 
     (b) Drum Drive Gear 
     The drum drive gears  71  are disposed to the left of the first side plate  66 L and to the left of the respective holes  85 A. The drum drive gears  71  each have a generally disc shape with gear teeth on its circumferential surface entirely. The drum drive gears  71  are rotatably supported by the first side plate  66 L. The drum drive gears  71  each have a hole  71 A and a plurality of, two, recesses  71 B. All of the drum drive gears  71  have the same or similar configuration, and therefore, one of the drum drive gears  71  will be described in detail. 
     The hole  71 A is defined in the center of the drum drive gear  71  in its diameter direction. The hole  71 A penetrates the drum drive gear  71  in the right-left direction. The hole  71 A has a generally circular shape in side view and its inside diameter may be substantially the same as an inside diameter of the hole  66 A of the first side plate  66 L. The holes  71 A are coincide with the respective holes  66 A of the first side plate  66 L in the right-left direction. 
     The hole  71 A has the recesses  71 B in an inner surface defining the hole  71 A in the diameter direction of the hole  71 A. The recesses  71 B may be grooves, each of which is recessed relative to the inner surface defining the hole  71 A in the diameter direction of the hole  71 A toward the exterior of the drum drive gear  71  and extends in the right-left direction. 
     (c) Translation Cam 
     The translation cam  72  is disposed in a right end portion of the frame  85 . The translation cam  72  overlaps the first side frame  41 L when projected in the up-down direction. The translation cam  72  has a generally flat plate shape extending in the front-rear direction. A front end portion of the translation cam  72  passes through the hole  85 B of the frame  85  and protrudes frontward beyond a front wall of the frame  85 . The translation cam  72  is movable in the front-rear direction between a pressing position (e.g., a position of the translation cam  72  depicted in  FIG. 9 ) and a non-pressing position (e.g., a position of the translation cam  72  depicted in  FIG. 6 ). When the translation cam  72  is located at the pressing position (refer to  FIG. 9 ), the translation cam  72  presses the main-body couplings  70  leftward. When the translation cam  72  is located at the non-pressing position (refer to  FIG. 6 ), the translation cam  72  does not press the main-body couplings  70 . The translation cam  72  is urged frontward toward the pressing position by the compression spring  87  at all times. When the front cover  8  is located at the closing position, a front end of the translation cam  72  is in contact with a rear surface of the front cover  8  and thus the translation cam  72  is pressed rearward against an urging force of the compression spring  87 , whereby the translation cam  72  is retained at the non-pressing position. The translation cam  72  has a plurality of, for example, four, holes  73  and includes a plurality of, for example, four, position switching portions  74 . 
     The holes  73  are spaced apart from each other in the front-rear direction while being defined side by side in the front-rear direction. The holes  73  penetrate the translation cam  72  in the right-left direction. The holes  73  are elongated in the front-rear direction, respectively. 
     All of the position switching portions  74  have the same or similar configuration, and therefore, one of the position switching portions  74  will be described in detail. The position switching portion  74  protrudes leftward in the right-left direction from a circumferential edge of a rear half portion of a corresponding hole  73  and extends along a circumferential direction of the hole  73 . The position switching portion  74  has a generally flat plate shape. The position switching portion  74  has an inclined surface  74 A and a parallel surface  74 B. 
     The inclined surface  74 A may be a front half portion of a left surface of the position switching portion  74 . The inclined surface  74 A is inclined leftward toward the rear. A front end of the inclined surface  74 A is contiguous with a left surface of the translation cam  72 . 
     The parallel surface  74 B is a rear half portion of the left surface of the position switching portion  74 . The parallel surface  74 B extends rearward contiguous with a rear end of the inclined surface  74 A. The parallel surface  74 B is parallel to the left surface of the translation cam  72 . 
     (d) Main-Body Couplings 
     All of the main-body couplings  70  have the same or similar configuration and are disposed at respective positions in the same or similar manner, and therefore, one of the main-body couplings  70  will be described in detail. The main-body coupling  70  is supported so as to be movable in the right-left direction while being disposed in the hole  71 A of a corresponding drum drive gear  71 . The main-body coupling  70  is disposed to the left of the lower portion  13 A of a corresponding process cartridge  13 . The main-body coupling  70  has a generally cylindrical column shape extending in the right-left direction. The main-body coupling  70  is movable between an engaged position (e.g., a position of the main-body coupling  70  depicted in  FIGS. 2 and 6 ) and a disengaged position (e.g., a position of the main-body coupling  70  depicted in  FIGS. 9 and 11 ). When the main-body coupling  70  is located at the engaged position (refer to  FIGS. 2 and 6 ), the main-body coupling  70  is in engagement with the coupling recess  16 C of the corresponding photosensitive drum  16 . When the main-body coupling  70  is located at the disengaged position (refer to  FIGS. 9 and 11 ), the main-body coupling  70  is positioned at a distance from the coupling recess  16 C of the corresponding photosensitive drum  16 . When the main-body coupling  70  is located at the engaged position, the main-body coupling  70  protrudes into the coupling recess  16 C of the corresponding photosensitive drum  16 . When the main-body coupling  70  is located at the disengaged position, the main-body coupling  70  is located receding from the coupling recess  16 C of the corresponding photosensitive drum  16 . The main-body coupling  70  includes a shaft portion  70 A, a plurality of, two, protruding portions  70 B, and a flange portion  70 C. 
     The shaft portion  70 A has a generally cylindrical column shape extending in the right-left direction. The shaft portion  70 A passes through the hole  71 A of the drum drive gear  71 , the hole  66 A of the first side plate  66 L, the hole  73  of the translation cam  72 , and the hole  85 A of the frame  85 . A second end portion E 2  (e.g., a right end portion) of the shaft portion  70 A protrudes rightward beyond a right wall of the frame  85  through the hole  85 A of the frame  85 . The shaft portion  70 A includes a plurality of, for example, two, protrusions  70 D. 
     The protrusions  70 D have a generally cylindrical column shape. The protrusions  70 D protrude from respective portions of a peripheral surface of a first end portion E 1  (e.g., a left end portion) of the shaft portion  70 A in a diameter direction of the shaft portion  70 A. The protrusions  70 D are disposed within the respective recesses  71 B of the drum drive gear  71  so as to be movable in the right-left direction but not to be movable in the circumferential direction of the drum drive gear  71 . With this configuration, the main-body coupling  70  is capable of rotating integral with the drum drive gear  71 . 
     The protruding portions  70 B have a generally cylindrical column shape. The protruding portions  70 B are disposed at respective portions closer to a circumferential edge of the second end portion E 2  in the diameter direction while protruding rightward from the second end portion E 2  of the shaft portion  70 A. 
     The flange portion  70 C has a generally plate shape. The flange portion  70 C protrudes in the diameter direction from a peripheral surface of the shaft portion  70 A at a substantially middle portion of the shaft portion  70 A in the right-left direction and extends in the circumferential direction of the shaft portion  70 A. 
     The second end portion E 2  of the main-body coupling  70  is disposed such that the second end portion E 2  is positioned between the first guide portion  65 L and the second guide portion  65 R and overlaps the first side frame  41 L when viewed in the up-down direction in a state where the main-body coupling  70  is located at the disengaged position. 
     (e) Compression Springs 
     The compression springs  88  are disposed in a contracted state while being disposed between the flange portions  70 C of the respective main-body couplings  70  and the first side plate  66 L. Thus, the main-body couplings  70  are urged rightward toward the engaged position at all times. 
     (3) Electric Supply Unit 
     The electric supply unit  64  is supported by a substantially middle portion of the second side plate  66 R in the up-down direction. The electric supply unit  64  includes a frame  86 , a power supply board  75 , a plurality of, for example, four, support shafts  93 , a translation cam  76 , a plurality of, for example, for, main-body electrodes  77 , and a plurality of, for example, four, compression springs  90 . 
     The frame  86  is disposed to the left of the second side plate  66 R. The frame  86  has a generally box shape extending in the front-rear direction. The frame  86  has a plurality of, for example, four, holes  86 A and a hole  86 B. The main-body electrodes  77  pass through the respective holes  86 A. The translation cam  76  passes through the hole  86 B. 
     The holes  86 A are defined in an upper end portion of a left wall of the frame  86 . The holes  86 A are disposed to the right of the respective developing electrodes  56  while facing the respective developing electrodes  56 . The holes  86 A are spaced apart from each other in the front-rear direction. The holes  86 A penetrate the left wall of the frame  86  in the right-left direction. 
     The hole  86 B is defined in a left end portion of the front wall of the frame  86 . The hole  86 B penetrates the front wall of the frame  86  in the front-rear direction. 
     (B) Power Supply Board 
     The power supply board  75  is disposed between the second side plate  66 R and the main-body electrodes  77  in a right end portion of the frame  86 . The power supply board  75  has a generally flat plate shape extending both in the up-down direction and in the front-rear direction. The power supply board  75  may be a circuit board including, for example, a transformer and a capacitor. The power supply board  75  is configured to convert electric power supplied from an input power source (not depicted) to a predetermined voltage using the transformer and store the voltage in the capacitor. By doing so, the power supply board  75  controls electric power to be applied on the main-body electrodes  77 . 
     (c) Support Shafts 
     The support shafts  93  are disposed to the right of the respective holes  86 A. The support shafts  93  have a generally cylindrical column shape. The support shafts  93  extend leftward from respective portions of a left surface of the second side plate  66 R. 
     (d) Translation Cam 
     The translation cam  76  is disposed in a left end portion of the frame  86 . The translation cam  76  overlaps the second side frame  41 R when projected in the up-down direction. The translation cam  76  has a generally flat plate shape extending in the front-rear direction. A front end portion of the translation cam  76  passes through the hole  86 B of the frame  86  and protrudes frontward beyond the front wall of the frame  86 . The translation cam  76  is movable in the front-rear direction between a pressing position (e.g., a position of the translation cam  76  depicted in  FIG. 9 ) and a non-pressing position (e.g., a position of the translation cam  76  depicted in  FIG. 6 ). When the translation cam  76  is located at the pressing position (refer to  FIG. 9 ), the translation cam  76  presses the main-body electrodes  77  rightward. When the translation cam  76  is located at the non-pressing position (refer to  FIG. 6 ), the translation cam  76  does not press the main-body electrodes  77 . The translation cam  76  is urged frontward toward the pressing position by the compression spring  89  at all times. When the front cover  8  is located at the closing position, a front end of the translation cam  76  is in contact with the rear surface of the front cover  8  and thus the translation cam  72  is pressed rearward against an urging force of the compression spring  89 , whereby the translation cam  76  is retained at the non-pressing position. The translation cam  76  has a plurality of, for example, four, holes  91  and a plurality of, for example, four, position switching portions  92 . 
     The holes  91  are spaced apart from each other in the front-rear direction. The holes  91  penetrate the translation cam  76  in the right-left direction. The holes  91  are elongated in the front-rear direction, respectively. 
     All of the position switching portions  92  have the same or similar configuration, and therefore, one of the position switching portions  92  will be described in detail. The position switching portion  92  protrudes rightward in the right-left direction from a circumferential edge of a rear half portion of a corresponding hole  91  and extends along a circumferential direction of the hole  91 . The position switching portions  92  has a generally flat plate shape. The position switching portion  92  has an inclined surface  92 A and a parallel surface  92 B. 
     The inclined surface  92 A may be a front half portion of a right surface of the position switching portion  92 . The inclined surface  92 A is inclined rightward toward the rear. A front end portion of the inclined surface  92 A is contiguous with a right surface of the translation cam  76 . 
     The parallel surface  92 B is a rear half portion of the right surface of the position switching portion  92 . The parallel surface  92 B extends rearward contiguous with a rear end of the inclined surface  92 A. The parallel surface  92 B is parallel to the right surface of the translation cam  76 . 
     (e) Main-Body Electrodes 
     All of the main-body electrodes  77  have the same or similar configuration and are disposed at respective positions in the same or similar manner, and therefore, one of the main-body electrodes  77  will be described in detail. The main-body electrode  77  is disposed to the left of the power supply board  75  while being supported by a corresponding support shaft  93  so as to be movable in the right-left direction. The main-body electrode  77  is disposed to the right of the lower portion  13 A of a corresponding process cartridge  13 . The main-body electrode  77  is movable between a contacting position (e.g., a position of the main-body electrode  77  depicted in  FIGS. 2 and 6 ) and a non-contacting position (e.g., a position of the main-body electrode  77  depicted in  FIGS. 9 and 11 ). When the main-body electrode  77  is located at the contacting position (refer to  FIGS. 2 and 6 ), the main-body electrode  77  is in contact with the developing electrode  56 . When the main-body electrode  77  is located at the non-contacting position (refer to  FIGS. 9 and 11 ), the main-body electrode  77  is not in contact with the developing electrode  56 . When the main-body electrode  77  is located at the contacting position, the main-body electrode  77  protrudes toward the developing electrode  56 . When the main-body electrode  77  is located at the non-contacting position, the main-body electrode  77  is located receding from the developing electrode  56 . The main-body electrode  77  includes a shaft portion  77 A and a flange portion  77 B. 
     The shaft portion  77 A extends in the right-left direction and has a generally cylindrical column shape with its left end closed. A left wall of the shaft portion  77 A has a curved surface of which middle portion in the diameter direction is convex toward the left. The shaft portion  77 A passes through the hole  91  of the translation cam  76  and the hole  86 A of the frame  86 . A second end portion E 3  (e.g., a left end portion) of the shaft portion  77 A protrudes leftward beyond a left wall of the frame  86  through the hole  86 A of the frame  86 . 
     The flange portion  77 B has a generally plate shape. The shaft portion  77 A protrudes in the diameter direction from a peripheral surface of a first end portion E 4  (e.g., a right end portion) and extends in a circumferential direction of the shaft portion  77 A. 
     The main-body electrode  77  is configured to apply a developing bias on a corresponding developing roller  18  via a corresponding developing electrode  56 . 
     The second end portion E 3  of the main-body electrode  77  is disposed such that the second end portion E 3  is positioned between the first guide portion  65 L and the second guide portion  65 R and overlaps the second side frame  41 R when viewed in the up-down direction in a state where the main-body electrode  77  is located at the non-contacting position. 
     (f) Compression Springs 
     The compression springs  90  are disposed in a contracted state while being disposed between the flange portions  77 B of the respective main-body electrodes  77  and the power supply board  75 . Thus, the main-body electrodes  77  are urged leftward toward the contacting position by the compression springs  90  at all times. 
     (4) First Guide Portion and Second Guide Portion 
     As depicted in  FIGS. 2 and 7 , the first guide portion  65 L is disposed to the right of the first side plate  66 L and above the driving unit  63 . The first guide portion  65 L has a generally rectangular column shape extending in the front-rear direction. The first guide portion  65 L has a first guide groove  65 A and a second guide groove  65 B and includes an engagement portion  65 C (refer to  FIGS. 8B and 8C ) and a plurality of, for example, two, rollers  65 D (refer to  FIG. 1 ). 
     The first guide groove  65 A of the first guide portion  65 L is recessed leftward relative to a right surface of the first guide portion  65 L and extends in the front-rear direction. The first guide groove  65 A has a generally rectangular shape in sectional view. The first guide groove  65 A has an open front end that opens toward the front. 
     The second guide groove  65 B of the first guide portion  65 L is recessed leftward relative to a left inner surface defining the first guide groove  65 A and extends in the front-rear direction. The second guide groove  65 B has a generally rectangular shape in sectional view. The second guide groove  65 B has a closed front end. 
     The engagement portion  65 C is disposed in the front of the second guide groove  65 B at a front end portion of the first guide portion  65 L. The engagement portion  65 C is recessed leftward relative to the left inner surface of the first guide groove  65 A. 
     As depicted in  FIGS. 7 and 10 , the rollers  65 D of the first guide portion  65 L are disposed in a front end portion of the first guide groove  65 A of the first guide portion  65 L while being spaced apart from each other in the front-rear direction. The rollers  65 D have a general disc shape and are rotatable on respective axes extending in the right-left direction. Upper end portions of the rollers  65 D protrude upward beyond a lower inner surface of the first guide groove  65 A. 
     As depicted in  FIGS. 2 and 7 , the second guide portion  65 R is disposed to the left of the second side plate  66 R and above the electric supply unit  64 . That is, the first guide portion  65 L and the second guide portion  65 R are disposed between the first side plate  66 L and the second side plate  66 R in the right-left direction. The second guide portion  65 R has a generally rectangular column shape extending in the front-rear direction. The second guide portion  65 R has a first guide groove  65 A and a second guide groove  65 B and includes a plurality of, for example, two, rollers  65 D. 
     The first guide groove  65 A of the second guide portion  65 R is recessed rightward relative to a left surface of the second guide portion  65 R and extends in the front-rear direction. The first guide groove  65 A has a generally rectangular shape in sectional view. The first guide groove  65 A has an open front end that opens toward the front. 
     The second guide groove  65 B of the second guide portion  65 R is recessed rightward relative to a right inner surface defining the first guide groove  65 A and extends in the front-rear direction. The second guide groove  65 B has a generally rectangular shape in sectional view. The second guide groove  65 B has a closed front end. 
     As depicted in  FIGS. 7 and 10 , the rollers  65 D of the second guide portion  65 R are disposed in a front end portion of the first guide groove  65 A of the second guide portion  65 R while being spaced apart from each other in the front-rear direction. The rollers  65 D have a general disc shape and are rotatable on respective axes extending in the right-left direction. Upper end portions of the rollers  65 D protrudes upward beyond a lower inner surface of the first guide groove  65 A. 
     (5) Pressing Portions 
     As depicted in  FIGS. 2 and 5 , the first pressing portion  60 L is disposed above the first guide portion  65 L. The first pressing portion  60 L is supported by a left end portion of the upper plate  67 . The first pressing portion  60 L includes a pressing lever  79 , a plurality of, for example, four, link members  80 , a rotating member  81 , and a tension spring  82  (refer to  FIG. 1 ). 
     The pressing lever  79  has a generally rectangular column shape extending in the front-rear direction. The pressing lever  79  includes a plurality of, for example, four, accommodating portions  79 A, a plurality of, for example, four, pressing members  83 , and a plurality of, for example, eight, compression springs  84 . 
     The accommodating portions  79 A are disposed above the urging portions  50  of the respective process cartridges  13 . The accommodating portions  79 A are spaced apart from each other in the front-rear direction. The accommodating portions  79 A are recessed upward relative to a lower surface of the pressing lever  79  and extend in the front-rear direction. The accommodating portions  79 A have a generally rectangular shape in side sectional view with its lower end opened. 
     The pressing members  83  are placed in the respective accommodating portions  79 A. The pressing members  83  have a generally box shape with its upper end opened and extend in the front-rear direction. 
     The compression springs  84  include four front compression springs  84 F and four rear compression springs  84 F. The front compression springs  84 F are disposed in a contracted state at front end portions of the respective accommodating portions  79 A. The rear compression springs  84 F are disposed in a contracted state at rear end portions of the accommodating portions  79 A. The compression springs  84  are coil springs that contract and expand in the up-down direction. An upper end of each compression spring  84  is in contact with a lower surface of an upper wall of a corresponding one of the accommodating portions  79 A. A lower end of each compression spring  84  is in contact with an upper surface of a lower wall of a corresponding one of the pressing members  83 . Thus, each pair of front compression springs  84 F and rear compression spring  84 F urges a corresponding pressing member  83  downward. An urging force of a pair of front compression spring  84 F and rear compression spring  84 F is stronger than an urging force of a pair of compression springs  54  of the urging portion  50  of the process cartridge  13 . 
     The link members  80  are disposed above the pressing lever  79  while being spaced apart from each other in the front-rear direction. Lower ends of the link members  80  are joined to an upper end portion of the pressing lever  79  such that the link members  80  are pivotable. Upper ends of the link members  80  are joined to the upper plate  67  such that the link members  80  are pivotable. 
     As depicted in  FIG. 1 , the rotating member  81  is disposed at a left end portion of an upper front end portion of the main body  2 . The rotating member  81  includes a rotating shaft  81 A, a first connecting portion  81 B, and a second connecting portion  81 C. 
     The rotating shaft  81 A has a generally cylindrical column shape extending in the right-left direction. The rotating shaft  81 A is rotatably supported by the first side plate  66 L. 
     The first connecting portion  81 B has a generally flat plate shape and extends rearward from the rotating shaft  81 A. 
     The second connecting portion  81 C has a generally flat plate shape and extends downward from the rotating shaft  81 A. The second connecting portion  81 C is rotatably connected with a front end portion of the pressing lever  79 . 
     The tension spring  82  may be a coil spring that expands and contracts in the up-down direction. An upper end of the tension spring  82  is connected with the first connecting portion  81 B. A lower end of the tension spring  82  is connected with a rear surface of the front cover  8 . The tension spring  82  expands to a length longer than its natural length in response to movement of the front cover  8  from the closing position to the exposing position. 
     As depicted in  FIG. 2 , the second pressing portion  60 R is disposed above the second guide portion  65 R. The second pressing portion  60 R is supported by a right end portion of the upper plate  67 . The second pressing portion  60 R has the same or similar configuration as the first pressing portion  60 L, and therefore, a detailed description will be omitted. 
     4. PROCEDURES FOR DETACHING AND ATTACHING PROCESS CARTRIDGE 
     (1) Detachment Procedure 
     Hereinafter, a procedure for detaching a process cartridge  13  will be described. In the description below, in a case where the same or similar components operate or function in the same or similar manner, a description will be made on one of the same or similar components. In order to detach a process cartridge  13  from the main body  2 , as depicted in  FIG. 10 , an operator moves the front cover  8  from the closing position to the exposing position. 
     In response to the movement of the front cover  8  from the closing position toward the exposing position, the translation cam  72  of the driving unit  63  moves frontward from the non-pressing position by an urging force of the compression spring  87  and the translation cam  76  of the electric supply unit  64  also moves frontward from the non-pressing position by an urging force of the compression spring  89 . 
     When the front cover  8  is tilted toward the front slightly from the closing position, as depicted in  FIG. 9 , the translation cam  72  of the driving unit  63  is located at the pressing position and the translation cam  76  of the electric supply unit  64  is also located at the pressing position. 
     In response to the movement of the translation cam  72  from the non-pressing position to the pressing position, the main-body coupling  70  moves leftward from the engaged position such that the flange portion  70 C slides over the inclined surface  74 A of the position switching portion  74 . Then, the flange portion  70   C comes  into contact with the parallel surface  74 B of the position switching portion  74  and thus the main-body coupling  70  is located at the disengaged position. 
     In response to the movement of the translation cam  76  from the non-pressing position to the pressing position, the main-body electrode  77  moves rightward from the contacting position while the flange portion  77 B slides over the inclined surface  92 A of the position switching portion  92 . Then, the flange portion  77 B comes into contact with the parallel surface  92 B of the position switching portion  92  and thus the main-body electrode  77  is located at the non-contacting position. 
     In this state, as depicted in  FIG. 11 , the main-body coupling  70  is located below the first side frame  41 L with overlapping the first side frame  41 L when projected in the up-down direction. Further, the second end portion E 2  of the main-body coupling  70  protrudes rightward beyond the first guide portion  65 L through the hole  85 A of the frame  85  of the driving unit  63 . 
     The main-body electrode  77  is located below the second side frame  41 R with overlapping the second side frame  41 R when projected in the up-down direction. Further, the second end portion E 3  of the main-body electrodes  77  protrudes leftward beyond the second guide portion  65 R through the hole  86 A of the frame  86  of the electric supply unit  64 . 
     Thereafter, as depicted in  FIG. 10 , the front cover  8  is further tilted toward the front. In response to this, the front cover  8  is further distanced from the translation cam  72  of the driving unit  63  and the translation cam  76  of the electric supply unit  64 . Finally, the front cover  8  reaches the exposing position and is retained at the exposing position. 
     In response to the movement of the front cover  8  to the exposing position, the tension spring  82  is pulled downward and frontward. 
     Thus, the first connecting portion  81 B is pulled downward and frontward by an urging force of the tension spring  82 . Therefore, the rotating member  81  rotates counterclockwise on the rotating shaft  81 A in left side view. 
     The pressing lever  79  is also pulled upward and frontward by the second connecting portion  81 C and thus moves upward and frontward in a translation manner. In response to the translation of the pressing lever  79 , the pressing member  83  moves upward and frontward to be separated from the urging portion  50 . 
     In this state, in the urging portion  50  of the first side wall  46 L, the contact member  53  is in contact with the upper surface of the first side frame  41 L. Therefore, the accommodating member  40  of the first side wall  46 L is urged upward relative to the contact member  53  by an urging force of the compression spring  54 . In the urging portion  50  of the second side wall  46 R, the contact member  53  is in contact with the upper surface of the second side frame  41 R. Therefore, the accommodating member  40  of the second side wall  46 R is urged upward relative to the contact member  53  by an urging force of the compression spring  54 . 
     Accordingly, the process cartridge  13  moves upward from the first position to the second position by an urging force of the urging portion  50  of the first side wall  46 L and an urging force of the urging portion  50  of the second side wall  46 R. In response to the upward movement of the process cartridge  13  from the first position to the second position, the contact member  53  of the urging portion  50  of the first side wall  46 L and the contact member  53  of the urging portion  50  of the second side wall  46 R move from the retracted position to the protruding position relative to each other. In other words, the process cartridge  13  moves from the first position to the second position by a reaction force that occurs due to pressing of the upper surface of the first side frame  41 L when the contact member  53  of the urging portion  50  of the first side wall  46 L moves from the retracted position to the protruding position and a reaction force that occurs due to pressing of the upper surface of the second side frame  41 R when the contact member  53  of the urging portion  50  of the second side wall  46 R moves from the retracted position to the protruding position. 
     Then, as depicted in  FIG. 11 , the drum support portion  49  of the first side wall  46 L of the process cartridge  13  is disengaged from the positioning recess  69 A of the first positioning plate  69 L and the drum support portion  49  of the second side wall  46 R of the process cartridge  13  is also disengaged from the positioning recess  69 A of the second positioning plate  69 R. Meanwhile, the photosensitive drum  16  of the process cartridge  13  moves upward to be separated from the intermediate transfer belt  29  such that a uniform spacing is provided in the up-down direction between the photosensitive drum  16  and the intermediate transfer belt  29  across the right-left direction. 
     Then, as depicted in  FIG. 8C , the operator turns the switching member  58  of the support frame  12  from the locking position to the unlocking position. 
     In response to this, the lock member  57  moves from the protruding position to the retracted position to disengage from the engagement portion  65 C. 
     Then, as depicted in  FIG. 12 , the operator pulls frontward the support frame  12  supporting the process cartridges  13  from the main body  2  to locate the support frame  12  at the outside position. 
     Thereafter, as depicted by a dashed line in  FIG. 12 , the operator pulls the process cartridge  13  upward to detach the process cartridge  13  from the support frame  12 . 
     Finally, the detachment of the process cartridge  13  from the main body  2  is completed. 
     (2) Attachment Procedure 
     Hereinafter, a procedure for attaching a process cartridge  13  will be described. In the description below, in a case where the same or similar components operate or function in the same or similar manner, a description will be made on one of the same or similar components. In order to attach a process cartridge  13  to the main body  2 , the operator operates the printer  1  in a reverse order to the detachment procedure. 
     More specifically, the operator inserts the process cartridge  13  into a corresponding opening  12 A of the support frame  12  from above. Thus, the process cartridge  13  is supported by the support frame  12 . 
     Then, as depicted in  FIG. 10 , the operator moves the support frame  12  supporting the process cartridges  13  into the main body  2  to locate the support frame  12  at the inside position. 
     Thereafter, as depicted in  FIG. 8B , the operator turns the switching member  58  of the support frame  12  from the unlocking position to the locking position. 
     In response to this, the lock member  57  moves from the retracted position to the protruding position to engage with the engagement portion  65 C. 
     Then, the operator moves the front cover  8  from the exposing position toward the closing position. 
     In response to the movement of the front cover  8  from the exposing toward the closing position, the tension spring  82  is restored and thus the tension of the tension spring  82  decreases. 
     Therefore, the tension of the tension spring  82  also decreases and the rotating member  81  rotates clockwise on the rotating shaft  81 A by an urging force of a coil spring (not depicted) in left side view. 
     In response to this, the pressing lever  79  is pressed downward and rearward by the second connecting portion  81 C and moves downward and rearward in a translation manner. In response to the translation of the pressing lever  79 , the pressing member  83  comes into contact with the upper surface of the urging portion  50  and thus the pressing member  83  presses the upper surface of the urging portion  50  downward. 
     Thus, the process cartridge  13  moves downward from the second position to the first position against an urging force of the compression spring  54  of the urging portion  50 . 
     In response to the downward movement of the process cartridge  13 , as depicted in  FIG. 2 , the drum support portion  49  of the process cartridge  13  comes into engagement with the positioning recess  69 A and the photosensitive drum  16  of the process cartridge  13  comes into contact with the upper surface of the intermediate transfer belt  29 . 
     Thereafter, the front cover  8  is further moved toward the closing position. In response to this, as depicted in  FIG. 9 , the front cover  8  comes into contact with the front end of the translation cam  72  of the driving unit  63  and the front end of the translation cam  76  of the electric supply unit  64  to press the translation cam  72  and the translation cam  76  rearward. 
     Thus, as depicted in  FIG. 6 , when the front cover  8  is located at the closing position, the translation cam  72  of the driving unit  63  is located at the non-pressing position and the translation cam  76  of the electric supply unit  64  is located at the non-pressing position. 
     In response to the movement of the translation cam  72  of the driving unit  63  from the pressing position to the non-pressing position, the main-body coupling  70  moves rightward from the disengaged position while the flange portion  70 C slides over the inclined surface  74 A of the position switching portion  74 . Then, the main-body coupling  70  comes into engagement with the coupling recess  16 C of the photosensitive drum  16  and thus the main-body coupling  70  is located at the engaged position. 
     In response to the movement of the translation cam  76  from the pressing position to the non-pressing position, the main-body electrode  77  moves leftward from the non-contacting position while the flange portion  77 B slides over the inclined surface  92 A of the position switching portions  92 . Then, the main-body electrode  77  comes into contact with the developing electrode  56  of the process cartridges  13  and thus the main-body electrode  77  is located at the contacting position. 
     Therefore, the attachment of the process cartridge  13  to the main body  2  is completed. In this state, the front end portion of the pressing lever  79  is in contact with the rear surface of the front cover  8 , whereby the pressing lever  79  is retained at the position. 
     Thereafter, a driving force is inputted to the drum drive gear  71  from a motor (not depicted) of the main body  2  and electric power supplied from the power supply board  75  is inputted into the developing electrode  56 . 
     Thus, the drum drive gear  71  starts rotating and the main-body coupling  70  starts rotating integral with the drum drive gear  71 . In response to this, the photosensitive drum  16  starts rotating on a rotating axis common to the main-body coupling  70  since the protruding portions  70 B of the main-body coupling  70  are in contact with the protrusions  16 D of the photosensitive drum  16 . 
     Further, a predetermined electric power is supplied to the developing roller  18  and the supply roller  19  of the process cartridge  13 . 
     5. CORRESPONDENCE BETWEEN FIRST ILLUSTRATIVE EMBODIMENT AND CLAIMED ELEMENTS 
     In the first illustrative embodiment, the up-down direction is an example of an orthogonal direction. The front-rear direction is an example of a sliding direction. The right-left direction is an example of an axial direction. The left is an example of one side in an axial direction. The right is an example of the other side in the axial direction. The printer  1  is an example of an image forming apparatus. Toner is an example of a developing agent. The toner image is an example of a developing agent image. The intermediate transfer belt  29  is an example of a transfer medium. The first flange member  16 B of the photosensitive drum  16  is an example of a driving-force receiving member. The urging portion  50  of the first side wall  46 L and the urging portion  50  of the second side wall  46 R are an example of a pressed portion. The developing electrode  56  is an example of an electrode member. The main-body coupling  70  is an example of a driving-force input member. The main-body electrode  77  is an example of an electric supply member. The translation cam  72  of the driving unit  63  is an example of a first movable member. The non-pressing position of the translation cam  72  is an example of a first position. The pressing position of the translation cam  72  is an example of a second position. The translation cam  76  of the electric supply unit  64  is an example of a second movable member. The non-pressing position of the translation cam  76  is an example of the first position. The pressing position of the translation cam  76  is an example of the second position. The compression spring  54  is an example of an urging member. 
     6. EFFECTS 
     (1) According to the printer  1  of the first illustrative embodiment, as depicted in  FIG. 3 , the first side frame  41 L and the second side frame  41 R of the support frame  12  that supports the process cartridges  13  each have the dimension in the up-down direction L 1  that is less than or equal to the dimension in the right-left direction L 2 . 
     Therefore, the first side frame  41 L and the second side frame  41 R of the support frame  12  may be reduced in size in the up-down direction. 
     Due to the achievement of the size reduction in the first side frame  41 L and the second side frame  41 R of the support frame  12  in the up-down direction, as depicted in  FIG. 11 , the structural components of the main body  2 , such as the first pressing portion  60 L, the second pressing portion  60 R, the driving unit  63 , and the electric supply unit  64 , and the structural components of the process cartridge  13 , such as the urging portion  50 , may be disposed in adjacent areas of the support frame  12  using spaces on both sides of the first side frame  41 L in the up-down direction and spaces on both sides of the second side frame  41 R in the up-down direction. 
     Accordingly, the printer  1  may be reduced in size. 
     Further, the weight of the first side frame  41 L and the second side frame  41 R may be reduced, thereby preventing the center of gravity of the main body  2  from being tilted frontward excessively when the support frame  12  is located at the outside position. Therefore, toppling of the main body  2  may be prevented or reduced when the support frame  12  is located at the outside position. 
     In a known printer, a support frame supports process cartridges by sandwiching the process cartridges between plate members extending in the up-down direction. Therefore, in order to reduce the size of the known printer in the right-left direction, generally, a thickness (e.g., a dimension in the right-left direction) of the plate members may be reduced. 
     In the printer  1  of the first illustrative embodiment, the dimension in the up-down direction L 1  of the first side frame  41 L and the dimension in the up-down direction L 1  of the second side frame  41 R are shortened to provide the spaces on the both sides of the first side frame  41 L in the up-down direction and the spaces on the both sides of the second side frame  41 R in the up-down direction. Through use of such spaces for arranging the structural components as described above, the above-described printer  1  may be further reduced in size than the known printer. 
     (2) According to the printer  1  of the first illustrative embodiment, as depicted in  FIGS. 2 and 5 , the dimension in the up-down direction L 1  of the first side frame  41 L and the dimension in the up-down direction L 1  of the second side frame  41 R may be between 5% and 30% inclusive (preferably, between 10% and 20% inclusive) of the dimension in the up-down direction L 4  of the process cartridges  13 . The left end portion of the process cartridge  13  is exposed from the first side frame  41 L when viewed from the left. The right end portion of the process cartridge  13  is exposed from the second side frame  41 R when viewed from the right. 
     Therefore, most of the left end portion and the right end portion of the process cartridge  13  (e.g., 70% or more of the dimension in the up-down direction, preferably, 90% or more of the dimension in the up-down direction) may be exposed from the first side frame  41 L and the second side frame  41 R, respectively. 
     With this configuration, the structural elements of the main body  2  may easily act on the left end portion and the right end portion of the process cartridge  13 , which are uncovered by the first side frame  41 L and the second side frame  41 R. 
     (3) According to the printer  1  of the first illustrative embodiment, as depicted in  FIG. 3 , the first side frame  41 L and the second side frame  41 R have a generally rectangular column shape extending in the front-rear direction. 
     Accordingly, rigidity of the first side frame  41 L and the second side frame  41 R may be ensured with the simple configuration. 
     (4) According to the above-described printer  1 , as depicted in  FIGS. 2 and 5 , the process cartridge  13  includes the lower portion  13 A and the upper portion  13 B. The lower portion  13 A is disposed below the first side frame  41 L and the second side frame  41 R and supports the photosensitive drum  16  in the state where the process cartridge  13  is supported by the support frame  12 . The upper portion  13 B is disposed above the first side frame  41 L and the second side frame  41 R while the process cartridge  13  is supported by the support frame  12 . 
     This configuration may enable to act the structural components of the main body  2 , such as the main-body couplings  70  and the main-body electrodes  77 , on the lower portion  13 A located below the first side frame  41 L and the second side frame  41 R easily. This configuration may further enable to act the structural components of the main body  2 , such as the first pressing portion  60 L and the second pressing portion  60 R, on the upper portion  13 B located above the first side frame  41 L and the second side frame  41 R easily. 
     Accordingly, flexible arrangement of the structural components of the main body  2  that act on the process cartridge  13  may be ensured. 
     (5) According to the above-described printer  1  of the first illustrative embodiment, as depicted in  FIG. 6 , the process cartridge  13  has the coupling recess  16 C in the left end portion of the lower portion  13 A and the developing electrode  56  at the right end portion of the lower portion  13 A. 
     Therefore, the process cartridge  13  receives a driving force from the main body  2  at the left side of the lower portion  13 A and electric power from the main body  2  at the right side of the lower portion  13 A. 
     Accordingly, when the process cartridge  13  receives a driving force and electric power from the main body  2 , the process cartridge  13  may be stably positioned with respect to the right-left direction. 
     (6) According to the printer  1  of the first illustrative embodiment, as depicted in  FIG. 2 , the main body  2  includes the main-body coupling  70  located to the left of the process cartridge  13  and the main-body electrode  77  located to the right of the process cartridge  13 . 
     Therefore, the main body  2  may input a driving force to the process cartridge  13  from the left of the process cartridge  13  while supplying electric power to the process cartridge  13  from the right of the process cartridge  13 . 
     Accordingly, when a driving force and electric power are inputted to the process cartridge  13  from the main body  2 , the process cartridge  13  may be retained stably. 
     This configuration may prevent or reduce interference of the main-body coupling  70  and the main-body electrode  77  with the process cartridge  13  when the support frame  12  is moved along the front-rear direction. 
     (7) According to the above-described printer  1 , as depicted in  FIG. 11 , the second end portion E 2  of the main-body coupling  70  is located between the first guide portion  65 L and the second guide portion  65 R when viewed in the up-down direction in the state where the main-body coupling  70  is located at the disengaged position. 
     Therefore, as depicted in  FIGS. 2 and 11 , the main-body coupling  70  may be movable between the engaged position and the disengaged position while the second end portion E 2  is located between the first guide portion  65 L and the second guide portion  65 R when viewed in the up-down direction. 
     With this configuration, in the state where the main-body coupling  70  is located at the disengaged position, the moving distance of the main-body coupling  70  may be shortened as compared with a case where the second end portion E 2  of the main-body coupling  70  is located closer to the left than the first guide portion  65 L. 
     Accordingly, a less space may be required for moving the main-body coupling  70 , whereby the size of the printer  1  may be reduced. 
     The second end portion E 2  of the main-body coupling  70  overlaps the first side frame  41 L when viewed in the up-down direction in the state where the main-body coupling  70  is located at the disengaged position. 
     Therefore, the main-body coupling  70  may be disposed effectively using the overlapping space in which the second end portion E 2  of the main-body coupling  70  overlaps the first side frame  41 L in the up-down direction. 
     (8) According to the printer  1  of the first illustrative embodiment, as depicted in  FIG. 11 , the translation cam  72  of the driving unit  63  overlaps the first side frame  41 L when viewed in the up-down direction. 
     Therefore, the translation cam  72  may be disposed effectively using the overlapping space in which the translation cam  72  of the driving unit  63  overlaps the first side frame  41 L in the up-down direction. 
     (9) According to the printer  1  of the first illustrative embodiment, as depicted in  FIG. 11 , the second end portion E 3  of the main-body electrodes  77  is located between the first guide portion  65 L and the second guide portion  65 R when viewed in the up-down direction in the state where the main-body electrode  77  is located at the non-contacting position. 
     Therefore, the main-body electrode  77  may be movable between the contacting position and the non-contacting position in the state where the second end portion E 3  is located between the first guide portion  65 L and the second guide portion  65 R when viewed in the up-down direction. 
     With this configuration, in the state where the main-body electrode  77  is located at the non-contacting position, the moving distance of the main-body electrode  77  may be shortened as compared with a case where the second end portion E 3  of the main-body electrode  77  is located closer to the right than the second guide portion  65 R. 
     Accordingly, a less space may be required for moving the main-body electrode  77 , whereby the size of the printer  1  may be reduced. 
     The second end portion E 3  of the main-body electrode  77  overlaps the second side frame  41 R when viewed in the up-down direction in the state where the main-body electrode  77  is located at the non-contacting position. 
     Therefore, the main-body electrodes  77  may be disposed effectively using the overlapping space in which the second end portion E 3  of the main-body electrode  77  overlaps the second side frame  41 R in the up-down direction. 
     (10) According to the printer  1  of the first illustrative embodiment, as depicted in  FIG. 11 , the translation cam  76  of the electric supply unit  64  overlaps the second side frame  41 R when viewed in the up-down direction. 
     Therefore, the translation cam  76  may be disposed effectively using the overlapping space in which the translation cam  76  of the electric supply unit  64  overlaps the second side frame  41 R in the up-down direction. 
     (11) According to the printer  1  of the first illustrative embodiment, as depicted in  FIG. 2 , the first guide portion  65 L and the second guide portion  65 R are disposed between the first side plate  66 L and the second side plate  66 R in the right-left direction. 
     Accordingly, the support frame  12  may be supported securely between the first side plate  66 L and the second side plate  66 R. 
     (12) According to the above-described printer  1 , as depicted in  FIG. 2 , the power supply board  75  may be disposed effectively between the second side plate  66 R and the main-body electrodes  77 . 
     (13) According to the printer  1  of the first illustrative embodiment, as depicted in  FIG. 5 , the dimension in the up-down direction L 1  of the first side frame  41 L and the dimension in the up-down direction L 1  of the second side frame  41 R are smaller than the dimension in the up-down direction L 4  of the coupling recess  16 C. 
     Therefore, the first side frame  41 L and the second side frame  41 R may have a smaller dimension in the up-down direction than the coupling recess  16 C. 
     Thus, more spaces may be ensured on the both sides of the first side frame  41 L in the up-down direction and on the both sides of the second side frame  41 R in the up-down direction. 
     Accordingly, the first pressing portion  60 L, the second pressing portion  60 R, the driving unit  63 , and the electric supply unit  64  may be disposed further effectively in the adjacent areas of the support frame  12  using the spaces on the both sides of the first side frame  41 L in the up-down direction and the spaces on the both sides of the second side frame  41 R in the up-down direction. 
     (14) According to the above-described printer  1 , as depicted in  FIG. 3 , the support frame  12  further includes the beam members  42  that connect the first side frame  41 L and the second side frame  41 R. 
     Accordingly, rigidity of the support frame  12  in the right-left direction may be ensured by the beam members  42 . 
     (15) According to the printer  1  of the first illustrative embodiment, as depicted in  FIG. 3 , the first side frame  41 L and the second side frame  41 R each have the engagement holes  45  with which the beam members  42  are engaged. 
     Therefore, the rigidity of the support frame  12  may be ensured in the right-left direction with the simple configuration in which the beam members  42  are engaged with the respective engagement holes  45  of the first side frame  41 L and the respective engagement holes  45  of the second side frame  41 R. 
     (16) According to the printer  1  of the first illustrative embodiment, as depicted in  FIG. 2 , the first pressing portion  60 L of the main body  2  presses the urging portion  50  of the first side wall  46 L. The second pressing portion  60 R of the main body  2  presses the urging portion  50  of the second side wall  46 R. The urging portion  50  of the first side wall  46 L overlaps the first side frame  41 L in the up-down direction. The urging portion  50  of the second side wall  46 R overlaps the second side frame  41 R in the up-down direction. 
     Therefore, the urging portion  50  of the first side wall  46 L and the urging portion  50  of the second side wall  46 R may be disposed effectively using the overlapping space in which the urging portion  50  of the first side wall  46 L overlaps the first side frame  41 L in the up-down direction and the overlapping space in which the urging portion  50  of the second side wall  46 R overlaps the second side frame  41 R in the up-down direction. 
     A pressing force of the first pressing portion  60 L is applied on the urging portion  50  of the first side wall  46 L from above and a reaction force from the first side frame  41 L acts on the urging portion  50  of the first side wall  46 L from below. A pressing force of the second pressing portion  60 R is applied on the urging portion  50  of the second side wall  46 R from above and a reaction force from the second side frame  41 R acts on the urging portion  50  of the second side wall  46 R from below. 
     Accordingly, the process cartridge  13  may be retained securely in the up-down direction. 
     (17) According to the printer  1  of the first illustrative embodiment, as depicted in  FIG. 9 , the main-body coupling  70  and the coupling recess  16 C are disengaged from each other in the middle of the movement of the front cover  8  from the closing position to the exposing position. Then, as depicted in  FIG. 10 , in the state where the main-body coupling  70  and the coupling recess  16 C are disengaged from each other, the pressing of the first pressing portion  60 L against the urging portion  50  of the first side wall  46 L is released and the pressing of the second pressing portion  60 R against the urging portion  50  of the second side wall  46 R is released. 
     Therefore, in the state where the main-body coupling  70  and the coupling recess  16 C are disengaged from each other, the process cartridge  13  may be moved from the first position to the second position. 
     Accordingly, the process cartridge  13  may be moved from the first position to the second position smoothly. 
     7. VARIATION OF SUPPORT FRAME 
     Hereinafter, referring to  FIGS. 13A and 13B , examples of variations of the support frame 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 reference numerals thereto. 
     (1) Outline of Variation of Support Frame 
     In the above-described support frame  12  of the first illustrative embodiment, the first side frame  41 L, the second side frame  41 R, and the beam members  42  define the openings  12 A into which the respective process cartridges  13  are inserted. The first side frame  41 L, the second side frame  41 R, and the beam members  42  all have a generally bar shape. 
     In one example of the variation, as depicted in  FIG. 13A , in a support frame  101 , a first side frame  102 L, a second side frame  102 R, and partition members  105  define openings  101 A. The first side frame  102 L and the second side frame  102 R have a generally bar shape, and the partition members  105  have a generally flat plate shape. 
     (2) Details of Variation of Support Frame 
     As depicted in  FIGS. 13A and 13B , a support frame  101  includes a first side frame  102 L, a second side frame  102 R, a first reinforcing member  106 L, a second reinforcing member  106 R, a front beam  103 , a rear beam  104 , and a plurality of, for example, three, partition members  105 . 
     The first side frame  102 L defines a left end of the support frame  101 . The first side frame  102 L may have a generally bar shape extending in the front-rear direction, and more specifically, have a generally rectangular column shape. The first side frame  102 L may be made of a hard resin material. The first side frame  102 L includes an accommodating portion  102 A, a plurality of slits  102 B, and a first guided portion  102 C. 
     The accommodating portion  102 A of the first side frame  102 L is disposed at a right end portion of the first side frame  102 L. The accommodating portion  102 A extends in the front-rear direction and has a generally rectangular cylindrical shape with its right end opened. The accommodating portion  102 A is disposed closer to the right than the first guide groove  65 A of the first guide portion  65 L. An upper surface of the accommodating portion  102 A is configured to come into contact with the contact member  53  of the first side wall  46 L of the process cartridge  13 . 
     The plurality of slits  102 B of the first side frame  102 L includes three slits  102 B defined in an upper wall of the accommodating portion  102 A and three slits  102 B defined in a lower wall of the accommodating portion  102 A. The slits  102 B defined in the upper wall of the accommodating portion  102 A are spaced apart from each other in the front-rear direction so as to divide an area of the upper wall of the accommodating portion  102 A into four equal areas in the front-rear direction. The slits  102 B defined in the upper wall of the accommodating portion  102 A of the first side frame  102 L are recessed leftward relative to a right end of the upper wall of the accommodating portion  102 A. The slits  102 B defined in the lower wall of the accommodating portion  102 A are spaced apart from each other in the front-rear direction so as to divide an area of the lower wall of the accommodating portion  102 A into four equal areas in the front-rear direction. The slits  102 B defined in the lower wall of the accommodating portion  102 A of the first side frame  102 L are recessed leftward relative to a right end of the lower wall of the accommodating portion  102 A. 
     The first guided portion  102 C of the first side frame  102 L is disposed at a left end portion of the first side frame  102 L. The first guided portion  102 C extends in the front-rear direction and has a generally rectangular column shape. The first guided portion  102 C is engaged in the first guide groove  65 A of the first guide portion  65 L. 
     The second side frame  102 R defines a right end of the support frame  101 . The second side frame  102 R may have a generally bar shape extending in the front-rear direction, and more specifically, have a generally rectangular column shape. The second side frame  102 R may be made of a hard resin material. The second side frame  102 R includes an accommodating portion  102 A, a plurality of slits  102 B, and a second guided portion  102 F. 
     The accommodating portion  102 A of the second side frame  102 R is disposed at a left end portion of the second side frame  102 R. The accommodating portion  102 A extends in the front-rear direction has a generally rectangular cylindrical shape with its left end opened. The accommodating portion  102 A is disposed closer to the left than the first guide groove  65 A of the second guide portion  65 R. An upper surface of the accommodating portion  102 A is configured to come into contact with the contact member  53  of the second side wall  46 R of the process cartridges  13 . 
     The plurality of slits  102 B of the second side frame  102 R includes three slits  102 B defined in an upper wall of the accommodating portion  102 A and three slits  102 B defined in a lower wall of the accommodating portion  102 A. The slits  102 B defined in the upper wall of the accommodating portion  102 A are spaced apart from each other in the front-rear direction so as to divide an area of the upper wall of the accommodating portion  102 A into four equal areas in the front-rear direction. The slits  102 B defined in the upper wall of the accommodating portion  102 A of the second side frame  102 R are recessed rightward relative to a left end of the upper wall of the accommodating portion  102 A. The slits  102 B defined in the lower wall of the accommodating portion  102 A are spaced apart from each other in the front-rear direction so as to divide an area of the lower wall of the accommodating portion  102 A into four equal areas in the front-rear direction. The slits  102 B defined in the lower wall of the accommodating portion  102 A of the first side frame  102 R are recessed rightward relative to a left end of the lower wall of the accommodating portion  102 A. 
     The second guided portion  102 F of the second side frame  102 R is disposed at a right end portion of the second side frame  102 R. The second guided portion  102 F extends in the front-rear direction and has a generally rectangular column shape. The second guided portion  102 F is engaged in the first guide groove  65 A of the second guide portion  65 R. 
     The first reinforcing member  106 L is fitted in the accommodating portion  102 A of the first side frame  102 L. The first reinforcing member  106 L has a generally bar shape extending in the front-rear direction, and more specifically, has a generally rectangular column shape. The first reinforcing member  106 L may be made of a metallic material having a higher stiffness, for example, stainless. 
     The second reinforcing member  106 R is fitted in the accommodating portion  102 A of the second side frame  102 R. The second reinforcing member  106 R has a generally bar shape extending in the front-rear direction, and more specifically, has a generally rectangular column shape. The second reinforcing member  106 R may be made of a metallic material having a higher stiffness, for example, stainless. 
     The front beam  103  defines a front end of the support frame  101 . The front beam  103  has a generally flat plate shape extending in the right-left direction and in the up-down direction. An upper end of the front beam  103  is located higher than an upper end of the first side frame  102 L and an upper end of the second side frame  102 R. The front beam  103  has a plurality of, for example, two, engagement holes  103 A. 
     One (e.g., the left engagement hole  103 A) of the engagement holes  103 A is defined in a left end portion of the front beam  103  and the other (e.g., the right engagement hole  103 A) of the engagement holes  103 A is defined in a right end portion of the front beam  103 . The engagement holes  103 A are recessed frontward relative to a rear surface of the front beam  103 . The engagement holes  103 A have a generally rectangular shape in front view. The left end portion of the front beam  103  is engaged with the front end portion of the first reinforcing member  106 L via the left engagement hole  103 A. The right end portion of the front beam  103  is engaged with the front end portion of the second reinforcing member  106 R via the right engagement hole  103 A. 
     The rear beam  104  defines a rear end of the support frame  101 . The rear beam  104  has a generally flat plate shape in the right-left direction and in the up-down direction. An upper end of the rear beam  104  is located higher than the upper end of the first side frame  102 L and the upper end of the second side frame  102 R. The rear beam  104  has a plurality of, two, engagement holes  104 A. 
     One (e.g., the left engagement hole  104 A) of the engagement holes  104 A is defined in a left end portion of the rear beam  104  and the other (e.g., the right engagement hole  104 A) of the engagement holes  104 A is defined in a right end portion of the rear beam  104 . The engagement holes  104 A are recessed rearward relative to a front surface of the rear beam  104 . The engagement holes  104 A have a generally rectangular shape. The left end portion of rear beam  104  is engaged with the rear end portion of the first reinforcing member  106 L via the left engagement hole  104 A. The right end portion of the rear beam  104  is engaged with the rear end portion of the second reinforcing member  106 R via the right engagement hole  104 A. 
     The partition members  105  are disposed between the front beam  103  and the rear beam  104  in the front-rear direction while being spaced apart from each other in the front-rear direction. The partition members  105  have a generally flat plate shape in the right-left direction. Upper ends of the partition members  105  are located higher than the upper ends of the front beam  103  and the rear beam  104 . The partition members  105  are engaged with the respective slits  102 B. The partition members  105  each have two cutouts  105 A. 
     One (e.g., the left cutout  105 A) of the cutouts  105 A is defined in a left end portion of a corresponding partition member  105  and is recessed rightward relative to a left end of the corresponding partition member  105 . The other of the cutouts  105 A (e.g., the right cutout  105 A) is defined in a right end portion of the corresponding partition member  105  and is recessed leftward relative to a right end of the corresponding partition member  105 . The left cutout  105 A is engaged with the first reinforcing member  106 L. The right cutout  105 A is engaged with the second reinforcing member  106 R. 
     (3) Correspondence Between Variation and Claimed Elements 
     In the support frame of the above-described variation, the accommodating portion  102 A of the first side frame  102 L is an example of a first cartridge-support portion. The accommodating portion  102 A of the second side frame  102 R is an example of a second cartridge-support portion. The partition member  105  is an example of a beam member. 
     (4) Effects 
     (4-1) According to the support frame  101  of the above-described variation, as depicted in  FIGS. 13A and 13B , the support frame  101  includes the first reinforcing member  106 L, which extends along the first side frame  102 L in the front-rear direction, and the second reinforcing member  106 R, which extends along the second side frame  102 R in the front-rear direction. 
     Therefore, the rigidity of the support frame  101  in the front-rear direction may be ensured by the first reinforcing member  106 L and the second reinforcing member  106 R while the support frame  101  may be reduced in size. 
     Accordingly, the above-described configuration may prevent or reduce the warping of the support frame  101  that may be caused when the support frame  101  is located at the outside position. 
     (4-2) According to the support frame  101  of the above-described variation, as depicted in  FIGS. 13A and 13B , the partition members  105  each have the cutout  105 A for engaging with the first reinforcing member  106 L and the cutout  105 A for engaging with the second reinforcing member  106 R. 
     Therefore, the rigidity of the support frame  101  in the front-rear direction may be ensured by the simple configuration in which the partition members  105  are engaged with the first reinforcing member  106 L and the second reinforcing member  106 R. 
     (4-3) According to the support frame  101  of the above-described variation, the effects that are the same as the effects obtained in the first illustrative embodiment may be obtained. 
     8. SECOND ILLUSTRATIVE EMBODIMENT 
     Referring to  FIGS. 14, 15, 16, 17, and 18 , 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 reference numerals thereto. 
     (1) Overview of Second Illustrative Embodiment 
     In the first illustrative embodiment, the process cartridge  13  includes the urging portion  50  of the first side wall  46 L and the urging portion  50  of the second side wall  46 R. The process cartridge  13  is configured to move from the first position to the second position due to application of the reaction force that is caused by pressing of the first side frame  41 L of the support frame  12  by the urging portion  50  of the first side wall  46 L and the reaction force that is caused by pressing of the second side frame  41 R of the support frame  12  by the urging portion  50  of the second side wall  46 R. 
     In the second illustrative embodiment, as depicted in  FIGS. 14 and 17 , a process cartridge  111  has no urging portion  50 . A first guide portion  112 L and a second guide portion  112 R are configured to move upward in synchronization with opening of the front cover  8 . 
     The process cartridge  111  is configured to be moved from the first position to the second position together with the support frame  101  by the first guide portion  112 L and the second guide portion  112 R. 
     (2) Details of Second Illustrative Embodiment 
     In the second illustrative embodiment, as depicted in  FIG. 16 , a process cartridge  111  has a configuration similar to the process cartridge  13  of the first illustrative embodiment except that the process cartridge  111  includes a projecting portion  111 A, instead of the urging portion  50 . 
     The projecting portion  111 A is disposed at a substantially middle portion of the first side wall  46 L in the up-down direction. The projecting portion  111 A protrudes leftward from a left surface of the first side wall  46 L. The projecting portion  111 A has a generally rectangular column shape in the front-rear direction. The projecting portion  111 A is also provided at the second side wall  46 R. 
     In the second illustrative embodiment, as depicted in  FIGS. 14 and 17 , a printer  110  have no first pressing portion  60 L nor second pressing portion  60 R. The printer  110  has a configuration similar to the printer  1  of the first illustrative embodiment except that the first guide portion  112 L and the second guide portion  112 R are movable in the up-down direction in the printer  110  and the printer  110  includes the support frame  101  of the above-described variation. 
     As depicted in  FIGS. 14 and 15 , the first guide portion  112 L is disposed above the driving unit  63 . The first guide portion  112 L has a generally rectangular column shape extending in the front-rear direction. The first guide portion  112 L has a guide groove  112 A and includes a plurality of, two, rollers  112 B, and a plurality of, four, link members  113 . 
     The guide groove  112 A of the first guide portion  112 L is recessed leftward relative to a right surface of the first guide portion  112 L and extends in the front-rear direction. The guide groove  112 A has a generally rectangular shape in sectional view. The guide groove  112 A has an open front end. 
     The rollers  112 B of the first guide portion  112 L are disposed in a front end portion of the guide groove  112 A of the first guide portion  112 L and are spaced apart from each other in the front-rear direction. The rollers  112 B have a generally disc shape and are rotatable on respective axes extending in the right-left direction. Upper end of the rollers  112 B protrude upward relative to a lower inner surface of the guide groove  112 A. 
     The link members  113  of the first guide portion  112 L are spaced apart from each other in the front-rear direction while being disposed below the first guide portion  112 L. Upper end portions of the link members  113  are connected to respective portions of a lower end portion of the first guide portion  112 L such that the link members  113  are rotatable. Lower end portions of the link members  113  are connected to respective portions of an upper wall of the driving unit  63  such that the link members  113  are rotatable. The frontmost link member  113  includes a connecting portion  113 A. 
     The connecting portion  113 A of the first guide portion  112 L has a generally flat plate shape and extends frontward from a lower end portion of the frontmost link member  113 . The connecting portion  113 A is connected with an upper end of the tension spring  82  disposed to the left of the connecting portion  113 A. 
     The second guide portion  112 R is disposed above the electric supply unit  64 . The second guide portion  112 R has a generally rectangular column shape extending in the front-rear direction. The second guide portion  112 R has a guide groove  112 A and includes a plurality of, two, rollers  112 B, and a plurality of, four, link members  113 . 
     The guide groove  112 A of the second guide portion  112 R is recessed rightward relative to a left surface of the second guide portion  112 R and extends in the front-rear direction. The guide groove  112 A has a generally rectangular shape in sectional view. The guide groove  112 A has an open front end. 
     The rollers  112 B of the second guide portion  112 R are disposed in a front end portion of the guide groove  112 A of the second guide portion  112 R and are spaced apart from each other in the front-rear direction. The rollers  112 B have a generally disc shape and are rotatable on respective axes extending in the right-left direction. Upper end of the rollers  112 B protrude upward relative to a lower inner surface of the guide groove  112 A. 
     The link members  113  of the second guide portion  112 R are spaced apart from each other in the front-rear direction while being disposed below the second guide portion  112 R. Upper end portions of the link members  113  are connected to respective portions of a lower end portion of the second guide portion  112 R such that the link members  113  are rotatable. Lower end portions of the link members  113  are connected to respective portions of an upper wall of the electric supply unit  64  such that the link members  113  are rotatable. The frontmost link member  113  includes a connecting portion  113 A. 
     The connecting portion  113 A of the second guide portion  112 R has a generally flat plate shape and extends frontward from a lower end portion of the frontmost link member  113 . The connecting portion  113 A is connected with an upper end of the other tension spring  82  disposed to the right of the connecting portion  113 A. 
     (3) Procedures for Detaching and Attaching Process Cartridge in Second Illustrative Embodiment 
     In the second illustrative embodiment, in order to detach a process cartridge  111  from the main body  2 , as depicted in  FIG. 17 , the operator moves the front cover  8  from the closing position to the exposing position in a similar manner to the first illustrative embodiment. In the description below, in a case where the same or similar components operate or function in the same or similar manner, a description will be made on one of the same or similar components. 
     When the front cover  8  is tilted toward the front slightly from the closing position, similar to the first illustrative embodiment, the translation cam  72  of the driving unit  63  is located at the pressing position and a translation cam  76  of the electric supply unit  64  is located at the pressing position. 
     Thus, the main-body coupling  70  is located at the disengaged position and the main-body electrode  77  is located at the non-contacting position. 
     In this state, as depicted in  FIG. 18 , the main-body coupling  70  is disposed below the first side frame  102 L with overlapping the first side frame  102 L when projected in the up-down direction. The right end portion of the main-body coupling  70  protrudes rightward beyond the first guide portion  112 L through a corresponding hole  85 A of the frame  85 . 
     The main-body electrode  77  is disposed below the second side frame  102 R with overlapping the second side frame  102 R when projected in the up-down direction. The left end portion of the main-body electrode  77  protrudes leftward beyond the second guide portion  112 R through a corresponding hole  86 A of the frame  86 . 
     Thereafter, as depicted in  FIG. 17 , in response to a further tilting of the front cover  8  toward the front to the exposing position, the connecting portion  113 A is pulled downward and frontward by an urging force of the tension spring  82 . Therefore, the frontmost link member  113  rotates clockwise on its lower end portion in side view. 
     Thus, the first guide portion  112 L and the second guide portion  112 R are pulled upward and frontward by the frontmost link member  113  and move upward and frontward in a translation manner. 
     Therefore, the process cartridge  111  moves upward from the first position to the second position in response to the movement of the first guide portion  112 L and the second guide portion  112 R. 
     In response to the upward movement of the process cartridge  111 , as depicted in  FIG. 18 , the photosensitive drum  16  of the process cartridge  111  moves upward to be separated from the intermediate transfer belt  29  such that a uniform spacing is provided in the up-down direction between the photosensitive drum  16  and the intermediate transfer belt  29  across the right-left direction. 
     Thereafter, the operator moves the support frame  101  supporting the process cartridges  111  frontward from the main body  2  to locate the support frame  101  at the outside position and then pulls the process cartridge  111  upward from the support frame  101  in a similar manner to the first illustrative embodiment. 
     Therefore, the detachment of the process cartridge  111  from the main body  2  is completed. 
     In order to attach a process cartridge  111  to the main body  2 , the operator operates the printer  110  in a reverse order to the detachment procedure. 
     More specifically, in a similar manner to the first illustrative embodiment, the operator inserts the process cartridge  111  into a corresponding opening  101 A of the support frame  101  and moves the support frame  101  supporting the process cartridges  111  to the inside position. Then, the operator moves the front cover  8  from the exposing position to the closing position. 
     Then, the first guide portion  112 L and the second guide portion  112 R move upward and rearward in a translation manner by weight of the process cartridges  111  and the support frame  101 . 
     Thus, as depicted in  FIGS. 14 and 15 , the drum support portion  49  of the process cartridge  111  comes into engagement with the positioning recess  69 A and thus the photosensitive drum  16  of the process cartridge  13  comes into contact with the upper surface of the intermediate transfer belt  29 . 
     Thereafter, in a similar manner to the first illustrative embodiment, in response to the movement of the front cover  8  to the closing position, the translation cam  72  of the driving unit  63  moves to the non-pressing position and the translation cam  76  of the electric supply unit  64  moves to the non-pressing position, the main-body coupling  70  moves to the engaged position, and the main-body electrode  77  moves to the contacting position. 
     Therefore, the attachment of the process cartridge  111  to the main body  2  is completed. 
     (4) Effects 
     According to the second illustrative embodiment, the effects that are the same as the effects obtained in the first illustrative embodiment may be obtained. 
     9. OTHER VARIATIONS 
     (1) In the above-described illustrative embodiments, the process cartridge  13 ,  111  as an example of a process cartridge includes the drum unit  14  and the developing unit  15  that are integral with each other. Nevertheless, in other embodiments, for example, another process cartridge including a drum unit including a photosensitive drum and a developing unit detachably attachable to the drum unit may be used as the process cartridge. 
     (2) In the above-described illustrative embodiments, the first side frame  41 L and the second side frame  41 R may be made of metal and have a hollow column extending in the sliding direction. 
     According to the variations, the rigidity of the first side frame  41 L and the second side frame  41 R may be ensured with the simple configuration.