Abstract:
A process unit includes: a photosensitive member; a developing unit; a developer cartridge; a guide portion; and an operation portion. The photosensitive member has a surface. The developing unit has a developing agent bearing member for bearing a developing agent to be supplied to the surface of the photosensitive member. The developer cartridge includes a casing defining an internal space for accommodating the developing agent, and a pressed portion provided at the casing and configured to be pressed by an external force. The developer cartridge is mountable on or detachable from the developing unit in a first direction, and further configured to be pressed in a second direction different from the first direction upon application of pressure to the pressed portion by the external force. The second direction is coincident with a direction of pressing the developing agent bearing member against the surface of the photosensitive member. The guide portion is shiftable between a first posture for guiding the developer cartridge to move relative to the developing unit in the first direction, and a second posture for guiding the developer cartridge to move relative to the developing unit in the second direction. The operation portion is configured to be operated to selectively shift the guide portion to one of the first posture and the second posture.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority from Japanese Patent Application No. 2010-180320 filed Aug. 11, 2010. The entire content of the priority application is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to an image forming device such as a laser printer and a process unit mounted in the image forming device. 
       BACKGROUND 
       [0003]    A conventional laser printer has a main casing, and, within the main casing, a process unit retaining a photosensitive drum and a developing roller is detachably mounted. A toner box in which toner is accommodated is mounted in the process unit. 
         [0004]    The photosensitive drum and the developing roller are disposed in the process unit such that a circumferential surface of the photosensitive drum is in contact with a circumferential surface of the developing roller. The process unit has a curved wall at a position opposite the photosensitive drum relative to the developing roller. The curved wall is formed so as to conform to an outline of the toner box. The process unit is further provided with a toner box accommodating chamber for accommodating the toner box at a position opposite the photosensitive drum and the developing roller relative to the curved wall. The toner box accommodating chamber includes a shutter movable along the curved wall. The curved wall is formed with a toner inlet port penetrating the curved wall. The curved wall has a surface confronting the shutter, and a seal member is affixed to the surface to encircle the toner inlet port. That is, the seal member is formed with a seal opening aligned with the toner inlet port. 
         [0005]    The toner box is mounted in the toner box accommodating chamber in alignment with the photosensitive drum and the developing roller. After the toner box has been mounted in the toner box accommodating chamber, the toner box is pressed toward the curved wall in the alignment direction, that is, a direction the same as a mounting direction of the toner box with respect to the toner box accommodating chamber. Then, the shutter is moved to a position displaced from the toner inlet opening. 
         [0006]    As a result, the shutter is displaced from a position between the seal member and the toner box, and the seal member and the toner box are brought into pressure contact with each other. Consequently, the periphery of the toner inlet port is sealed between the curved wall and the toner box by the seal member. In this state, the interior of the toner box and a space in which the photosensitive drum and the developing roller are accommodated have a fluid communication with each other through the toner inlet port, allowing toner to fluidly circulate between the space and the interior of the toner box. 
       SUMMARY 
       [0007]    However, with the above-described structure, the mounting direction of the toner box is the same as the pressing direction of the toner box with respect to the curved wall. If the mounting direction and the pressing direction can be independently determined, enhanced degree of freedom in design of the process unit can be obtained. However, if the mounting direction is different from the pressing direction, a structure for allowing the toner box to move both in the mounting direction and the pressing direction is required. Because, when the toner box is mounted in the toner box accommodating chamber, movement of the toner box in the mounting direction should be allowed, and when the toner box is positioned in the toner box accommodating chamber, movement of the toner box in the pressing direction should be allowed. 
         [0008]    In view of the foregoing, it is an object of the present invention to provide a process unit allowing a developer cartridge to move in two directions and capable of reliably moving the developer cartridge in each direction, and an image forming device provided with the process unit. 
         [0009]    In order to attain the above and other objects, the present invention provides a process unit including: a photosensitive member; a developing unit; a developer cartridge; a guide portion; and an operation portion. The photosensitive member has a surface. The developing unit has a developing agent bearing member for bearing a developing agent to be supplied to the surface of the photosensitive member. The developer cartridge includes a casing defining an internal space for accommodating the developing agent, and a pressed portion provided at the casing and configured to be pressed by an external force. The developer cartridge is mountable on or detachable from the developing unit in a first direction, and further configured to be pressed in a second direction different from the first direction upon application of pressure to the pressed portion by the external force. The second direction is coincident with a direction of pressing the developing agent bearing member against the surface of the photosensitive member. The guide portion is shiftable between a first posture for guiding the developer cartridge to move relative to the developing unit in the first direction, and a second posture for guiding the developer cartridge to move relative to the developing unit in the second direction. The operation portion is configured to be operated to selectively shift the guide portion to one of the first posture and the second posture. 
         [0010]    According to another aspect, the present invention provides an image forming device including: a main casing; and the above-described process unit. The process unit is detachably attached to the main casing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The particular features and advantages of the present invention as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
           [0012]      FIG. 1  is a cross-sectional view of a color printer according to one embodiment of the present invention; 
           [0013]      FIG. 2  is a perspective view of the color printer shown in  FIG. 1 , showing a drawer unit that has been pulled outward from a main casing of the color printer; 
           [0014]      FIG. 3  is a perspective view of the drawer unit shown in  FIG. 1 , from which all toner cartridges are removed; 
           [0015]      FIG. 4  is a perspective view of an operation guide unit shown in  FIG. 3 ; 
           [0016]      FIG. 5  is a partial cross-sectional view of the drawer unit shown in  FIG. 3  and a left side view of the toner cartridge; 
           [0017]      FIG. 6  is a perspective view of the toner cartridge shown in  FIG. 5 ; 
           [0018]      FIG. 7  is an exploded perspective view of the toner cartridge shown in  FIG. 6 ; 
           [0019]      FIG. 8A  is a schematic view of the operation guide unit along with a left side view of the toner cartridge shown in  FIG. 5  and a partial cross-sectional view of the drawer unit shown in  FIG. 5 , wherein the toner cartridge is mounted in the drawer unit and a shutter of the toner cartridge is at a closed position; 
           [0020]      FIG. 8B  is a partial cross-sectional view of the drawer unit at a state shown in  FIG. 8A . 
           [0021]      FIG. 9A  is a schematic view of the operation guide unit along with a left side view of the toner cartridge shown in  FIG. 5  and a partial cross-sectional view of the drawer unit shown in  FIG. 5 , wherein the toner cartridge is mounted in the drawer unit, the shutter is at an open position, and the toner cartridge is at a first position; 
           [0022]      FIG. 9B  is a partial cross-sectional view of the drawer unit at a state shown in  FIG. 9A ; 
           [0023]      FIG. 10  is a left side view of the toner cartridge shown in  FIG. 5  and a partial cross-sectional view of the drawer unit shown in  FIG. 5 , wherein the toner cartridge is mounted in the drawer unit, the shutter is at the open position, and the toner cartridge is at a second position; 
           [0024]      FIG. 11  is a cross-sectional view of the drawer unit shown in  FIG. 1 , showing a state that developing rollers are in contact with photosensitive drums, respectively; 
           [0025]      FIG. 12  is a cross-sectional view of the drawer unit shown in  FIG. 1 , showing a state that the developing rollers are separated from the respective photosensitive drums; 
           [0026]      FIG. 13  is a perspective view of a toner cartridge according to a modification; 
           [0027]      FIG. 14  is a perspective view of an operation guide unit provided in a drawer unit in which the toner cartridge shown in  FIG. 13  is mounted; 
           [0028]      FIG. 15  is a partial cross-sectional view of the drawer unit in which the toner cartridge shown in  FIG. 13  is mounted, wherein the operation guide unit is in a first posture; and 
           [0029]      FIG. 16  is a partial cross-sectional view of the drawer unit in which the toner cartridge shown in  FIG. 13  is mounted, wherein the operation guide unit is in a second posture. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    Next, an image forming device according to one embodiment of the present invention will be described while referring to the accompanying drawings. 
         [0031]    1. Structure of Color Printer 
         [0032]    As shown in  FIG. 1 , the image forming device according to the embodiment is a tandem-type color printer  1 . As shown in  FIGS. 1 and 2 , the color printer  1  includes a main casing  2 . A drawer unit  3  as a process unit is mounted inside the main casing  2 . The main casing  2  has a front portion at which a front cover  4  is provided. The front cover  4  is movable between an open position and a closed position. When the front cover  4  is in the open position, the drawer unit  3  can be moved horizontally between an accommodated position inside the main casing  2  (a position shown in  FIG. 1 ) and a pulled-out position outside the main casing  2  (a position shown in  FIG. 2 ). 
         [0033]    The terms “upward”, “downward”, “upper”, “lower”, “above”, “below”, “right”, “left”, “front”, “rear” and the like will be used throughout the description assuming that the color printer  1  is disposed in an orientation in which it is intended to be used. In the following description, a side of the color printer  1  on which the front cover  4  is provided (right side in  FIG. 1 ) will be referred to as a front side of the color printer  1 . Top, bottom, left, and right sides of the color printer  1  in the following description will be based on the reference point of a user viewing the color printer  1  from the front side. Directions related to the drawer unit  3  and a toner cartridge  11 , described later, that is mounted in the drawer unit  3  will be referenced based on their positions when mounted in the main casing  2 , unless otherwise specified. Note that the front cover  4  has been omitted from  FIG. 2 . 
         [0034]    The drawer unit  3  includes a drawer frame  31  installing four photosensitive drums  5 , four chargers  6 , four developing units  7 , and four cleaners  10 . 
         [0035]    As shown in  FIG. 1 , the four photosensitive drums  5  are rotatably retained in the drawer unit  3 . The photosensitive drums  5  are capable of rotating about axes extending in a left-to-right direction. The four photosensitive drums  5  are respectively provided for the colors black, yellow, magenta, and cyan. The photosensitive drums  5  are arranged parallel to each other at regular intervals in a front-to-rear direction in the order black, yellow, magenta, and cyan from the front. 
         [0036]    The four chargers  6  are also retained in the drawer unit  3 . The chargers  6  have a one-on-one correspondence to the four photosensitive drums  5  and are disposed diagonally upward and rearward of the corresponding photosensitive drums  5 . Each charger  6  is a Scorotron charger that includes a discharge wire and a grid, for example. 
         [0037]    The four developing units  7  are also retained in the drawer unit  3 . The four developing units  7  also have a one-on-one correspondence to the four photosensitive drums  5 , and are disposed diagonally above and forward of the corresponding photosensitive drums  5 . Each developing unit  7  includes a developing unit frame  8 , and a developing roller  9  accommodated in the developing unit frame  8 . Each developing roller  9  is disposed so as to contact the corresponding photosensitive drum  5  and is capable of rotating about an axis extending in the left-to-right direction. 
         [0038]    The four cleaners  10  are also retained in the drawer unit  3 . The four cleaners  10  also have a one-on-one correspondence to the four photosensitive drums  5  and are disposed rearward of the corresponding photosensitive drums  5 . The cleaners  10  function to remove paper dust deposited on surfaces of the photosensitive drums  5 . 
         [0039]    A space  12  is defined in the drawer unit  3  above each developing unit  7 . The toner cartridge  11  is mounted in the space  12 . Sufficient free space above the drawer unit  3  is acquired for mounting the toner cartridges  11  in the spaces  12  by pulling the drawer unit  3  outward to the pulled-out position. The toner cartridges  11  supply toner to the corresponding developing units  7 . 
         [0040]    An exposure unit  13  is provided in the main casing  2  above the drawer unit  3 . The exposure unit  13  irradiates four laser beams corresponding to the four colors used by the color printer  1 . 
         [0041]    As each photosensitive drum  5  rotates, the corresponding charger  6  applies a uniform charge to the surface of the photosensitive drum  5 . Subsequently, the exposure unit  13  irradiates laser beams for selectively exposing the surfaces of the photosensitive drums  5 . This exposure selectively removes charge from the surfaces of the photosensitive drums  5 , forming electrostatic latent images thereon. When the electrostatic latent image carried on the surface of the photosensitive drum  5  rotates to a position opposite the corresponding developing roller  9 , the developing roller  9  supplies toner to the electrostatic latent image, thereby forming a toner image on the surface of the photosensitive drum  5 . 
         [0042]    Four LED arrays may be provided for the four photosensitive drums  5  in place of the exposure unit  13 . 
         [0043]    A sheet cassette  14  accommodating sheets of paper P is disposed at a bottom section of the main casing  2 . Each sheet P accommodated in the sheet cassette  14  is conveyed onto a conveying belt  15  by various rollers. The conveying belt  15  confronts the four photosensitive drums  5  from below. Four transfer rollers  16  are disposed inside the conveying belt  15  at positions confronting the photosensitive drums  5  through an upper portion of the conveying belt  15 . When the sheet P is conveyed onto the conveying belt  15 , the conveying belt  15  carries the sheet P sequentially through positions between the conveying belt  15  and each of the photosensitive drums  5 . As the sheet P passes beneath each photosensitive drum  5 , the toner image carried on the surface of the photosensitive drum  5  is transferred onto the sheet P. 
         [0044]    A fixing unit  17  is provided at a position downstream of the conveying belt  15  with respect to a direction that the sheet P is conveyed. After toner images are transferred onto the sheet P, the sheet P is conveyed to the fixing unit  17 , where the toner images are fixed to the sheet P by heat and pressure. After the toner images have been fixed in the fixing unit  17 , various rollers discharge the sheet P onto a discharge tray  18  provided on a top surface of the main casing  2 . 
         [0045]    Four main casing pressure mechanisms  19  are provided in the main casing  2  so as to be disposed below the exposure unit  13  and above the drawer unit  3  accommodated in the main casing  2 . The main casing pressure mechanisms  19  have a one-on-one correspondence to the four toner cartridges  11 . Each of the main casing pressure mechanisms  19  includes two sets of a main casing pressure member  20  and an urging member  21 . The urging member  21  is for urging the main casing pressure member  20  downward. Each set of the main casing pressure member  20  and the urging member  21  is movable between a lower position and an upper position. In the lower position, each main casing pressure member  20  contacts a pressed portion  66  (described later) provided at an upper surface of the toner cartridge  11  to press the pressed portion  66 . In the upper position, the main casing pressure member  20  is separated upward from the drawer unit  3 . 
         [0046]    2. Drawer Unit 
         [0047]    (1) Drawer Frame 
         [0048]    As shown in  FIG. 3 , the drawer unit  3  has the drawer frame  31 . The drawer frame  31  is configured of a pair of side plates  32  and  33  arranged parallel to each other and separated in the left-to-right direction, a front beam  134  bridging the front ends of the side plates  32  and  33 , and a rear beam  135  bridging the rear ends of the side plates  32  and  33 . The overall structure of the drawer frame  31  is square-shaped in a plan view. 
         [0049]    The respective groups of four photosensitive drums  5 , chargers  6 , developing units  7  and cleaners  10  (see  FIG. 1 ) are all held together between the side plates  32  and  33  on the left and right sides thereof. The spaces  12  in which the toner cartridges  11  are mounted are defined between the side plates  32  and  33  above the corresponding developing units  7 . In other words, the side plates  32  and  33  hold the photosensitive drums  5 , the chargers  6 , the developing units  7 , and the cleaners  10 . Further, the side plates  32  and  33  oppose each other in the left-to-right direction, with gaps formed therebetween to allocate the spaces  12  in which the toner cartridges  11  are mounted. 
         [0050]    (2) Operation Guide Unit 
         [0051]    Four operation guide units  34  are provided at the left side plate  32  at positions corresponding to the four spaces  12 . 
         [0052]    As shown in  FIGS. 3 and 4 , each operation guide unit  34  includes a disk-shaped main portion  35 , an operation portion  36  and a guide portion  37 . The main portion  35 , the operation portion  36 , and the guide portion  37  are integrally formed. The operation portion  36  is a protrusion protruding leftward from a left (outer) surface of the main portion  35 . The guide portion  37  is provided on a right (inner) surface of the main portion  35 . The guide portion  37  is formed in a disk-shape concentric with the main portion  35 , having a diameter smaller than that of the main portion  35 . 
         [0053]    The guide portion  37  is formed with a guide groove  38 . The guide portion  37  has a circumferential surface, from which the guide groove  38  extends along the diameter of the guide portion  37 . The guide groove  38  does not penetrate the guide portion  37  in a diametrical direction of the guide portion  37 . That is, the guide groove  38  has end portions in the diametrical direction, one of the end portions is open and remaining one of the end portions is closed. With this configuration, the operation guide unit  34  has an opposing portion  39  positioned between the circumferential surface of the guide portion  37  and the guide groove  38  in the diametrical direction. The opposing portion  39  functions as a positioning and retaining portion for guided portions  64  (described later) provided in the toner cartridge  11 . 
         [0054]    As indicated by an imaginary line shown in  FIG. 4 , the left side plate  32  has an upper portion formed with four circular fitting portions  40  at positions corresponding to the four spaces  12 . Each fitting portion  40  has a diameter slightly greater than that of the guide portion  37 . The guide portion  37  is rotatably fitted into the fitting portion  40 , thereby rotatably holding the operation guide unit  34  in the left side plate  32 . When the operation guide unit  34  is held in the left side plate  32 , the operation portion  36  is positioned at a left side of the left side plate  32 , and the guide portion  37  is positioned at a right side of the left side plate  32 . The operation guide unit  34  is angularly movable between a first posture and a second posture, as described later. 
         [0055]    Further, as indicated by the imaginary line shown in  FIG. 4 , an inner surface (right side surface) of the left side plate  32  is formed with four installation grooves  132 . The installation groove  132  functions to accurately install the guided portions  64  of the toner cartridge  11  in the guide groove  38 . Each installation groove  132  extends upward from an upper edge of the corresponding fitting portion  40 . The installation groove  132  has a lower end portion having a width the same as that of the guide groove  38 . The installation groove  132  has a width gradually increasing toward the top of the left side plate  32 . With this configuration, the installation groove  132  is formed in a Y-shape as viewed from a right side. 
         [0056]    (3) Developing Unit Frame 
         [0057]    As shown in  FIG. 3 , the four developing unit frames  8  are disposed at regular intervals in the front-to-rear direction and span between the side plates  32  and  33 . The developing unit frames  8  define the spaces  12  provided for mounting the toner cartridges  11 . 
         [0058]    As shown in  FIG. 5 , a developing chamber  41  is formed in each developing unit frame  8  for accommodating the developing roller  9 . The developing chamber  41  has a lower open side opposing the corresponding photosensitive drum  5 . The developing roller  9  is disposed in the bottom of the developing chamber  41  near the open side thereof. Further, the developing roller  9  contacts the corresponding photosensitive drum  5  so as to press the photosensitive drum  5  in downward and rearward (that is, in a second direction described later). 
         [0059]    The developing unit frame  8  also has a plate-shaped partitioning wall  42  positioned between the developing chamber  41  and the space  12 . The partitioning wall  42  curves in an arc shape with its convex side facing the developing chamber  41 . The partitioning wall  42  partitions the interior of the developing unit frame  8  into the developing chamber  41  and the space  12  formed above the developing chamber  41 . Three rectangular openings  43  are formed in a circumferential center of the partitioning wall  42 . The openings  43  are formed at positions opposing three cartridge communication holes  58  ( FIG. 7 , described later) formed in the toner cartridge  11  when the toner cartridge  11  is mounted in the space  12 . 
         [0060]    (4) Shutter Drive Assembly 
         [0061]    As shown in  FIG. 5 , a shutter drive assembly  44  is movably disposed above the partitioning wall  42  for driving a shutter  73  described later. 
         [0062]    The shutter drive assembly  44  is formed into an arcuate plate shaped, with the convex side facing the developing chamber  41 . The arcuate shape of the shutter drive assembly  44  substantially conforms to the shape of the partitioning wall  42 . The shutter drive assembly  44  has a bottom surface provided with a rack gear  45 . The shutter drive assembly  44  has a top surface provided with shutter drive protrusions  46  at positions corresponding to shutter drive openings  88  ( FIG. 7 ) described later. 
         [0063]    3. Toner Cartridge 
         [0064]    (1) Casing 
         [0065]    As shown in  FIGS. 6 and 7 , the toner cartridge  11  includes a casing  51  for accommodating toner. The casing  51  is formed of resin in a substantially hollow semicircular column shape and is elongated in the left-to-right direction. More specifically, the casing  51  defines an internal space for accommodating toner, and includes a rectangular top surface  52 , an arcuate surface  53 , a fixing surface  54 , a rear surface  55 , a left side surface  56 , and a right side surface  57 . 
         [0066]    The top surface  52  is elongated in the left-to-right direction. The arcuate surface  53  is connected to a front edge of the top surface  52  and has a substantially semicircular shape in a cross-section with a convex side facing downward. The fixing surface  54  extends parallel to the top surface  52  and protrudes rearward from a rear edge of the arcuate surface  53 . The rear surface  55  bridges a rear edge of the top surface  52  and a rear edge of the fixing surface  54 . The left side surface  56  bridges respective left edges of the top surface  52 , the arcuate surface  53 , the fixing surface  54  and the rear surface  55 . The right side surface  57  bridges respective right edges of the top surface  52 , the arcuate surface  53 , the fixing surface  54 , and the rear surface  55 . 
         [0067]    As shown in  FIG. 7 , the arcuate surface  53  is formed with the three cartridge communication holes  58  at positions slightly rearward of a lowest end thereof. The cartridge communication holes  58  are rectangular in shape and elongated in the left-to-right direction and are spaced at intervals in the left-to-right direction. The cartridge communication holes  58  provide communication between the interior and exterior of the casing  51 . 
         [0068]    Further, the arcuate surface  53  is formed with narrow slit-shaped relief grooves  59 . The relief grooves  59  extend in a circumferential direction of the arcuate surface  53  and are formed one on each of left and right sides of each cartridge communication hole  58 . 
         [0069]    As shown in  FIG. 6 , the arcuate surface  53  has a front edge on which a plurality of positioning protrusions  60  is formed. The positioning protrusions  60  are spaced at intervals in the left-to-right direction. Each positioning protrusion  60  has a hook shape, extending forward, then bending and extending upward (see also  FIG. 5 ). 
         [0070]    As shown in  FIGS. 6 and 7 , the left side surface  56  is formed with a boss  61  protruding leftward therefrom. The boss  61  is formed in a columnar shape. As shown in  FIG. 6 , a drive force generation gear  62  is rotatably supported to the boss  61 . The drive force generation gear  62  has a left side surface on which a disk plate  63  is fixedly provided. The disk plate  63  is provided with the two guided portions  64 . The two guided portions  64  are provided at positions in confrontation with each other, interposing the boss  61  therebetween. That is, the two guided portions  64  are spaced apart from each other at an angle of 180 degrees about the boss  61 . Each of the guided portions  64  has a columnar shape, and protrudes leftward from the disk plate  63 . 
         [0071]    Note that the drive force generation gear  62 , the disk plate  63 , and the guided portion  64  have been omitted from  FIG. 7 . 
         [0072]    Further, as shown in  FIG. 6 , a triangle portion as viewed from a left side is cut-out from a corner defined by the top surface  52 , the arcuate surface  53 , and the left side surface  56 , thereby forming a slant surface  65  ( 65 L) extending diagonally above and rearward from the arcuate surface  53  to the top surface  52 . In the same manner, a triangle portion as viewed from a right side is cut-out from a corner defined by the top surface  52 , the arcuate surface  53 , and the right side surface  57 , thereby forming a slant surface  65  ( 65 R) extending diagonally above and rearward from the arcuate surface  53  to the top surface  52 . 
         [0073]    Further, the top surface  52  of the casing  51  has left and right end portions at which the pressed portions  66  are provided, as shown in  FIG. 6 . That is, two pressed portions  66  are provided at the top surface  52 ; one of the pressed portions  66  is provided at the left end portion of the top surface  52 , and remaining one of the pressed portions  66  is provided at the right end portion of the top surface  52 . Each of the pressed portions  66  is formed in a square-frustum shape. The top surface  52  and the pressed portions  66  are integrally formed. 
         [0074]    As shown in  FIG. 7 , the toner cartridge  11  further includes toner seals  71  affixed to the arcuate surface  53  of the casing  51 , a shutter cover  72  disposed so as to cover the arcuate surface  53 , and the shutter  73  disposed between the arcuate surface  53  and the shutter cover  72 . 
         [0075]    (2) Toner Seal 
         [0076]    Each of the toner seals  71  is provided for each cartridge communication hole  58 . The toner seal  71  has a sheet-like form and is formed with an opening  74  at a position corresponding to the cartridge communication hole  58 . The toner seals  71  are fixed to the arcuate surface  53  of the casing  51  so that the openings  74  are aligned and in communication with the corresponding cartridge communication holes  58  and, hence, the toner seals  71  encircle the cartridge communication holes  58 . Further, as shown in  FIG. 9A , annular frame seals  102  are disposed on the partitioning wall  42  at positions confronting the corresponding toner seals  71  so as to surround the periphery of the corresponding openings  43 . The frame seal  102  has an opening having a shape and dimension coincident with those of the opening  74  of the toner seal  71 . 
         [0077]    (3) Shutter Cover 
         [0078]    The shutter cover  72  is curved to conform to the arcuate surface  53  of the casing  51 . The shutter cover  72  is formed of a resin film. The shutter cover  72  has a width in the left-to-right direction substantially equal to a width of the arcuate surface  53  in the left-to-right direction. Thus, the shutter cover  72  covers the arcuate surface  53  across substantially the entire width in the left-to-right direction. 
         [0079]    As shown in  FIG. 7 , the shutter cover  72  has a front end portion formed with a plurality of positioning openings  80  spaced apart from each other in the left-to-right direction. As shown in  FIG. 6 , the positioning protrusions  60  formed on the arcuate surface  53  of the casing  51  are engaged with the positioning openings  80 . More specifically, the positioning openings  80  are formed in the front end portion of the shutter cover  72  and are arrayed in the left-to-right direction corresponding to the positioning protrusions  60 . Further, the positioning openings  80  are formed of a sufficient size for inserting the positioning protrusions  60 . After the positioning protrusions  60  are inserted into the corresponding positioning openings  80 , top edges of the positioning openings  80  engage the positioning protrusions  60 . 
         [0080]    The shutter cover  72  has a rear end portion folded back to conform to the fixing surface  54  of the casing  51 . A plurality of screw insertion through-holes  81  are formed in this rear end portion of the shutter cover  72  at intervals in the left-to-right direction, as shown in  FIG. 7 . As shown in  FIGS. 5 and 6 , the shutter cover  72  is attached to the casing  51  by engaging the positioning protrusions  60  with the respective positioning openings  80 , and by inserting screws  82  through all of the screw insertion through-holes  81  and screwing tips of the screws  82  into the fixing surface  54  of the casing  51 . 
         [0081]    As shown in  FIG. 7 , the shutter cover  72  is formed with shutter cover communication holes  83  at positions corresponding to the toner seals  71 . Each of the shutter cover communication holes  83  has a rectangular shape and is elongated in the left-to-right direction. Further, the shutter cover communication hole  83  has an open area greater than that of the cartridge communication hole  58  so as to expose the cartridge communication hole  58  in its entirety. 
         [0082]    Further, the shutter cover  72  is formed with guide slits  85  elongated in the front-to-rear direction (circumferential direction of the shutter cover  72 ) at positions corresponding to the relief grooves  59  formed in the casing  51 . The guide slit  85  has a front-to-rear length greater than or equal to that of the relief groove  59 . The guide slits  85  also has a left-to-right width greater than or equal to that of the relief groove  59 . Each guide slit  85  confronts the corresponding relief groove  59  in its entirety. 
         [0083]    (4) Shutter 
         [0084]    As shown in  FIG. 7 , the shutter  73  curves along the arcuate surface  53  of the casing  51 . The shutter  73  is formed of a resin film having a width in the left-to-right direction slightly smaller than that of the shutter cover  72 . The shutter  73  has a dimension along the circumferential direction of the arcuate surface  53  greater than that of the toner seal  71 . Further, the dimension of the shutter  73  along the circumferential direction of the arcuate surface  53  is set such that the shutter  73  does not contact the fixing surface  54  and the positioning protrusions  60  when moving between an open position and a closed position described later. 
         [0085]    The shutter  73  is formed with two shutter drive openings  88  separated by a prescribed interval in a circumferential direction of the shutter  73  at positions opposing each relief groove  59  in the casing  51 . The distance between the two shutter drive openings  88  in the circumferential direction is set such that all shutter drive openings  88  confront the corresponding relief grooves  59  and confront and communicate with the corresponding guide slits  85  formed in the shutter cover  72 , regardless of whether the shutter  73  is in the open position or the closed position. 
         [0086]    The shutter  73  is interposed between the arcuate surface  53  of the casing  51  and the shutter cover  72 . While held between the arcuate surface  53  and the shutter cover  72 , the shutter  73  can move between the open position and the closed position. 
         [0087]    When the shutter  73  is in the open position, a rear edge of the shutter  73  is interposed between a front edge portion of the toner seal  71  and the shutter cover  72 . Therefore, each cartridge communication hole  58  formed in the casing  51  and the opening  74  formed in the corresponding toner seal  71  are made open, while being in communication between the cartridge communication holes  58  and the shutter cover communication holes  83 . This provides communication between the interior and exterior of the casing  51 . 
         [0088]    On the other hand, in the closed position, the shutter  73  is positioned farther rearward than the open position. When the shutter  73  is in the closed position, the rear edge of the shutter  73  is positioned slightly rearward from rear edges of the shutter cover communication holes  83 . As a result, the shutter  73  covers the cartridge communication holes  58  formed in the casing  51  and the openings  74  formed in the toner seals  71  in their entirety, blocking communication between the interior and exterior of the casing  51 . At this time, the toner seals  71  are interposed between the shutter  73  and the arcuate surface  53  of the casing  51 . 
         [0089]    4. Drive Force Transmission Mechanism 
         [0090]    Within the drawer frame  31 , a plurality of drive force transmission mechanisms  91  each corresponding to each shutter drive assembly  44  is provided, as shown in  FIG. 5 . The drive force transmission mechanism  91  functions to transmit a drive force generated by the drive force generation gear  62  provided in the toner cartridge  11  to the rack gear  45  of the shutter drive assembly  44 . Each drive force transmission mechanism  91  includes a first transmission gear  92 , a second transmission gear  93 , and a third transmission gear  94 . When the toner cartridge  11  is in the space  12 , the first transmission gear  92  is meshedly engageable with the drive force generation gear  62 , the second transmission gear  93  is meshedly engageable with the first transmission gear  92 , and the third transmission gear  94  is meshedly engageable with the second transmission gear  93  and the rack gear  45 . The first to third transmission gears  92 ,  93 ,  94  are rotatably supported to the left side plate  32  of the drawer frame  31 . 
         [0091]    When the drive force generation gear  62  rotates, a rotational force is transmitted to the first transmission gear  92  from the drive force generation gear  62 , thereby rotating the first transmission gear  92 . The rotational force transmitted to the first transmission gear  92  is further transmitted to the rack gear  45  through the second transmission gear  93  and the third transmission gear  94 . With this configuration, the shutter drive assembly  44  can move in the front-to-rear direction along the partitioning wall  42 , and, as described later, the shutter  73  can move between the open position and the closed position in association with the movement of the shutter drive assembly  44 . The drive force generation gear  62 , the first transmission gear  92 , the second transmission gear  93 , the third transmission gear  94 , and the rack gear  45  constitute a drive mechanism (gear train) for moving the shutter  73  between the open position and the closed position. 
         [0092]    5. Drawer Unit Pressure Member 
         [0093]    Further, a plurality of a pair of drawer unit pressure members  101  (a left drawer unit pressure member  101 L, a right drawer unit pressure member  101 R (not shown)) each corresponding to each toner cartridge  11  (space  12 ) is provided in the drawer frame  31 , as shown in  FIG. 5 . The pair of the drawer unit pressure members  101  functions to press the toner cartridge  11  toward the corresponding developing units  7 . The drawer unit pressure member  101  is formed of a wire spring. One of the pair of drawer unit pressure members  101 L has a lower end portion that is supported to the left side plate  32  of the drawer frame  31 , and remaining one of the pair of the drawer unit pressure members  101 R has a lower end portion that is supported to the right side plate  33  of the drawer frame  31 . In other words, the four drawer unit pressure members  101 L are provided at the left side plate  32 , and another four drawer unit pressure members  101 R are provided at the right side plate  33 . Each drawer unit pressure member  101  has a shape extending upward from the lower end portion, then bending diagonally above and rearward, and then folding diagonally above and forward. More specifically, the left drawer unit pressure member  101 L has a portion  107  ( 107 L) extending diagonally above and rearward, and the portion  107 L is inclined relative to a horizontal plane at an angle the same as that of the slant surface  65  ( 65 L) of the casing  51  of the toner cartridge  11 . Likewise, the right drawer unit pressure member  101 R has a portion  107  ( 107 R, not shown) extending diagonally above and rearward, and the portion  107 R is inclined relative to a horizontal plane at an angle the same as that of the slant surface  65  ( 65 R) of the casing  51  of the toner cartridge  11 . 
         [0094]    6. Mounting and Dismounting of Toner Cartridge 
         [0095]    (1) Mounting of Toner Cartridge 
         [0096]    While the drawer unit  3  (drawer frame  31 ) is pulled outward from the main casing  2  and disposed at the pulled-out position ( FIG. 2 ), the toner cartridge  11  is mounted in or dismounted from the space  12  from above. Note that mounting of the toner cartridge  11  in the space  12  implies attachment of the toner cartridge  11  relative to the developing unit  7 . 
         [0097]    When the toner cartridge  11  is not mounted in the space  12 , as shown in  FIG. 8B , the operation guide unit  34  is in the first posture. When the operation guide unit  34  is in the first posture, the guide groove  38  extends in a first direction (an upper-to-lower direction) and the opposing portion  39  is disposed below the guide groove  38 . As shown in  FIG. 8A , when the operation guide unit  34  is in the first posture, the operation portion  36  extends diagonally above and forward from a lower rear side. At this time, the shutter drive protrusion  46  positioned closer to a front side among the pairs of shutter drive protrusions  46  formed in the shutter drive assembly  44  protrude upward along a substantially vertical direction, while the shutter drive protrusion  46  positioned closer to a rear side among the pairs of shutter drive protrusions  46  protrude in a direction angled upward and forward. 
         [0098]    When the toner cartridge  11  is not mounted in the drawer unit  3 , the shutter  73  is in the closed position. Further, as shown in  FIG. 5 , the two guided portions  64  are aligned in the first direction (upper-to-lower direction). 
         [0099]    When the toner cartridge  11  is mounted in the space  12 , the two guided portions  64  are inserted into the guide groove  38  from above through the installation groove  132  formed in the left side plate  32 . Since the guide groove  38  extends in the first direction, the toner cartridge  11  moves in the first direction in association with movement of the guided portions  64  along the guide groove  38 . Movement of the guided portions  64  is stopped by bringing the leading guided portion  64  into contact with the opposing portion  39 . In other words, when the operation guide unit  34  is in the first posture, the opposing portion  39  serves as a positioning portion for determining the position of the leading guided portion  64  (the position of the toner cartridge  11 ). 
         [0100]    Incidentally, it is not necessary for the two guided portions  64  to be accurately aligned in the first direction. The two guided portions  64  may be aligned in a direction slightly inclined relative to the first direction. Even if the guided portions  64  are inclined relative to the first direction, when the guided portions  64  are inserted into the installation groove  132  from above to be moved along the installation groove  132 , slant surfaces formed in the upper end portion of the installation groove  132  guides the two guided portions  64  so as to be aligned in the first direction. 
         [0101]    Movement of the toner cartridge  11  in the first direction brings the shutter drive protrusions  46  into engagement with the shutter drive openings  88  through the guide slits  85 . Thus, the toner cartridge  11  is brought into contact with the shutter drive assembly  44 . As a result, mounting of the toner cartridge  11  in the space  12  can be achieved. When the toner cartridge  11  is mounted in the space  12 , the portions  107 L,  107 R are respectively brought into contact with the slant surfaces  65 L,  65 R, so that the toner cartridge  11  can be pressed downward and rearward by the pair of drawer unit pressure members  101 L,  101 R with a relatively small force. 
         [0102]    Subsequently, the operation guide unit  34  is shifted to the second posture from the first posture, as shown in  FIGS. 9A and 9B . That is, a user holds the operation portion  36  by his/her fingers to angularly rotate the operation guide unit  34  in a counterclockwise direction as viewed from a left side at an angle of 135 degrees so that, as shown in  FIG. 9A , the operation guide unit  34  is shifted to the second posture in which the operation portion  36  extends horizontally from the first posture in which the operation portion  36  is inclined and extends diagonally above and forward from the lower rear side. 
         [0103]    In association with the shift of the operation guide unit  34  to the second posture from the first posture, the guide groove  38  extends in the second direction that inclines diagonally downward and rearward, as shown in  FIG. 9B . Accordingly, a direction for guiding the guided portions  64  by the guide groove  38  is shifted to the second direction from the first direction. Further, in association with the angular rotation of the operation guide unit  34 , the guided portions  64  are angularly moved about the boss  61 . In association with the angular movement of the guided portions  64 , the drive force generation gear  62  and the disk plate  63  rotate in the counterclockwise direction as viewed from the left side. Rotation of the drive force generation gear  62  generates a rotational force. The rotational force is transmitted to the third transmission gear  94  through the first transmission gear  92  and the second transmission gear  93 , and thus, the third transmission gear  94  rotates in a clockwise direction as viewed from the left side. In association with the rotation of the third transmission gear  94 , the shutter drive assembly  44  moves forward to a position forward of the openings  43  from a position opposing the openings  43 . In association with the movement of the shutter drive assembly  44 , the shutter  73  moves forward from the closed position along with the shutter drive assembly  44 . The shutter  73  is then positioned at the open position. 
         [0104]    When the operation guide unit  34  is in the second posture, the opposing portion  39  confronts the leading guided portion  64  at a position diagonally above and forward of the leading guided portion  64 . Because of the position of the opposing portion  39 , the guided portions  64  cannot be pulled out of the guide groove  38 . That is, when the operation guide unit  34  is in the second posture, the opposing portion  39  serves as the retaining portion for retaining the guided portions  64  in the guide groove  38 . 
         [0105]    At this time, the toner cartridge  11  is positioned at a first position in which the toner cartridge  11  is located at a position relatively far from the partitioning wall  42 . A slight gap is formed between the toner cartridge  11  and the frame seals  102 . Further, the shutter cover  72  is not pressed against the toner seals  71 . That is, the shutter cover  72  is not in contact with the toner seals  71 . 
         [0106]    Then, the drawer unit  3  is moved to the accommodated position inside the main casing  2  ( FIG. 1 ). When the drawer unit  3  is located at the accommodated position, each set of the main casing pressure member  20  and the urging member  21  moves downward to the lower position from the upper position, each main casing pressure member  20  is brought into contact with the corresponding pressed portion  66  provided at the upper surface of the toner cartridge  11 , and each pressed portion  66  is pressed downward by the corresponding main casing pressure member  20 . 
         [0107]    Since the guide groove  38  is inclined in the second direction ( FIG. 9B ), a pressure force that the pressed portions  66  are pressed downward is converted to a force directed downward and rearward. Hence, the toner cartridge  11  moves downward and rearward, that is, moves in the second direction. With this movement, as shown in  FIG. 10 , the toner cartridge  11  is positioned at a second position in which the toner cartridge  11  is located at a position relatively close to the partitioning wall  42 . Each of the toner seals  71  has a protruding portion that protrudes outward through the corresponding shutter cover communication hole  83 . The protruding portions of the toner seals  71  are brought into pressure contact with the corresponding frame seals  102  from above and front, that is, from upstream of the frame seals  102  in the second direction. Hence, the toner seals  71  and the frame seals  102  are compressed. Therefore, while the toner seals  71  and the frame seals  102  seal any gaps formed between the partitioning wall  42  and the shutter cover  72 , the openings  74  formed in the toner seals  71  are in communication with the corresponding openings  43  through the opening formed in the corresponding frame seals  102 . 
         [0108]    Thereafter, when the front cover  4  ( FIG. 1 ) is moved to the closed position, an image forming operation can be started. 
         [0109]    (2) Dismounting of Toner Cartridge 
         [0110]    For dismounting the toner cartridge  11  from the drawer unit  3 , the front cover  4  is moved to the open position, and the drawer unit  3  is moved from the accommodated position to the pulled-out position. Then, the operation guide unit  34  is shifted to the first posture from the second posture. That is, the operation guide unit  34  is angularly rotated in a clockwise direction as viewed from the left side at an angle of 135 degrees. In association with the angular rotation of the operation guide unit  34 , the guide groove  38  extends in the first direction. By performing, in reverse order, the above described operation when the toner cartridge  11  is mounted in the space  12 , the shutter  73  is moved to the closed position from the open position. 
         [0111]    Subsequently, the toner cartridge  11  is removed upward from the space  12 . Because the guide groove  38  extends in the first direction, the guided portions  64  are guided upward. When the toner cartridge  11  has been removed from the drawer unit  3 , the shutter  73  is in the closed position. Accordingly, there is no risk of toner spilling out of the casing  51  when the toner cartridge  11  is removed. 
         [0112]    7. Pressing and Releasing Developing Roller 
         [0113]    Further, the color printer  1  has a mechanism for separating the developing rollers  9  from the corresponding photosensitive drums  5  when an image forming operation is not performed, in order to restrain degradation of the photosensitive drums  5  and the developing rollers  9 . 
         [0114]    As shown in  FIG. 3 , each of the developing rollers  9  is provided with a roller shaft  103 . Each roller shaft  103  has end portions each protruding outward of the developing unit frame  8  and further protruding outward of the side plates  32 ,  33 . 
         [0115]    As shown in  FIGS. 11 and 12 , within the main casing  2 , two separation cams  104  are provided at positions confronting outer surfaces of the side plates  32 ,  33 , respectively, when the drawer unit  3  is in the accommodated position. Each of the separation cams  104  is formed in a plate shape and extends in the front-to-rear direction. The separation cams  104  are linearly movable in the front-to-rear direction. The separation cams  104  confront the end portions of the roller shafts  103  protruding from the side plates  32 ,  33  from below. Further, each of the separation cams  104  has an upper surface having four separating portions  105 . Each separating portion  105  is formed in a trapezoidal-shape as viewed from a left (right) side. The four separating portions  105  are arranged at intervals in the front-to-rear direction. Each of the separating portions  105  has a slant surface  106  extending diagonally above and rearward from each front portion of each separating portion  105 . 
         [0116]    When the developing roller  9  is in contact with the photosensitive drum  5 , as shown in  FIG. 11 , each separating portion  105  of each separation cam  104  is disposed rearward of the corresponding roller shaft  103 . Further, end portions of each roller shaft  103  contact from above portions of the corresponding separation cams  104 , the portions being positioned forward of the corresponding separating portions  105 . In this state, when the separation cams  104  move forward, the slant surfaces  106  are brought into contact with the end portions of the corresponding roller shafts  103 . When the separation cams  104  further move forward, as shown in  FIG. 12 , the end portions of each roller shaft  103  move onto the corresponding slant surfaces  106 . As a result, each roller shaft  103  is pressed upward and forward by the corresponding slant surfaces  106 . Hence, each of the developing rollers  9  moves upward and forward, and is separated from the corresponding photosensitive drum  5 . 
         [0117]    When the separation cams  104  move rearward while the developing rollers  9  are spaced apart from the corresponding photosensitive drums  5 , the slant surface  106  of each separating portion  105  moves rearward of the end portion of the corresponding roller shaft  103 , and separates therefrom. As described above, the toner cartridge  11  (toner seals  71 ) has been pressed relative to the developing unit frame  8  (frame seals  102 ) from above and front, that is, from upstream of the shutter cover communication holes  83  in the second direction. Therefore, when pressure of the roller shaft  103  by the slant surfaces  106  is released, the developing roller  9  moves in the second direction. As a result, the developing roller  9  is brought into contact with the corresponding photosensitive drum  5  in the second direction. 
         [0118]    8. Operations and Effects 
         [0119]    (1) Operation and Effect 1 
         [0120]    As described above, the toner cartridge  11  includes the casing  51  and the pressed portions  66 . Movement of the casing  51  in the first direction (upper-to-lower direction) allows the casing  51  to be mounted in or dismounted from the developing unit  7 . Further, the pressed portions  66  are pressed by the main casing pressure members  20 , so that the toner cartridge  11  is pressed relative to the developing unit  7  in the second direction different from the first direction (that is, in a direction that inclines diagonally below and rearward). 
         [0121]    In order to guide movement of the toner cartridge  11  in the first direction and the second direction, the operation guide unit  34  (the guide portion  37 ) is provided on the left side plate  32  of the drawer frame  31 . The operation guide unit  34  (the guide portion  37 ) can be shifted between the first posture and the second posture. Further, the operation guide unit  34  includes the operation portion  36  that is operated to shift the operation guide unit  34  between the first posture and the second posture. The operation guide unit  34  in the first posture guides movement of the toner cartridge  11  in the first direction, while the operation guide unit  34  in the second posture guides movement of the toner cartridge  11  in the second direction. 
         [0122]    The operation portion  36  is operated to selectively shift the posture of the operation guide unit  34  either in the first posture or in the second posture, thereby allowing the toner cartridge  11  to selectively move either in the first direction or in the second direction. The first posture of the operation guide unit  34  reliably guides the toner cartridge  11  to move in the first direction, and the second posture of the operation guide unit  34  reliably guides the toner cartridge  11  to move in the second direction. 
         [0123]    (2) Operation and Effect 2 
         [0124]    The casing  51  of the toner cartridge  11  is formed with cartridge communication holes  58  for supplying toner accommodated inside the casing  51  to the developing unit  7 . Further, the toner cartridge  11  includes the shutter  73  movable between the open position in which the cartridge communication holes  58  are open and the closed position in which the cartridge communication holes  58  are closed. 
         [0125]    Further, in order to move the shutter  73  between the open position and the closed position, the drive mechanism (gear train) including the drive force generation gear  62 , the first transmission gear  92 , the second transmission gear  93 , the third transmission gear  94 , and the rack gear  45  is provided. With this drive mechanism, when the operation portion  36  is operated to shift the operation guide unit  34  from the first posture to the second posture, the shutter  73  is moved to the open position from the closed position. When the operation portion  36  is operated to shift the operation guide unit  34  from the second posture to the first posture, the shutter  73  is moved to the closed position from the open position. 
         [0126]    Accordingly, in association with the operation of the operation portion  36 , the operation guide unit  34  can be shifted between the first posture and the second posture, and the shutter  73  can be moved between the open position and the second position. 
         [0127]    (3) Operation and Effect 3 
         [0128]    The periphery of the cartridge communication hole  58  is surrounded by the toner seal  71 . When the shutter  73  is in the closed position, the toner seals  71  are interposed between the casing  51  and the shutter  73 . Therefore, when the shutter  73  is in the closed position, toner leakage to a portion between the casing  51  and the shutter  73  through the cartridge communication holes  58  can be prevented. 
         [0129]    Even if the toner seals  71  are interposed between the casing  51  and the shutter  73 , while the operation guide unit  34  is in the first posture, the toner cartridge  11  is not pressed in the second direction. Hence, the casing  51  and the shutter  73  are not excessively in pressure contact with the toner seals  71 . In addition, the shutter  73  does not pressingly contact the frame seals  102 . Therefore, when the operation guide unit  34  is shifted to the second posture from the first posture and the shutter  73  moves to the open position from the closed position, the operation portion  36  can be operated with a relatively small force. 
         [0130]    (4) Operation and Effect 4 
         [0131]    A plurality of the main casing pressure members  20  is provided within the main casing  2 . When the drawer unit  3  is accommodated in the main casing  2 , each main casing pressure member  20  presses the corresponding toner cartridge  11  toward the corresponding developing unit  7 . Prior to accommodating the drawer unit  3  in the main casing  2 , the operation guide unit  34  has been shifted to the second posture from the first posture. Hence, when the main casing pressure member  20  presses the toner cartridge  11 , the toner cartridge  11  is pressed toward the corresponding developing unit  7  in the second direction. As a result, the toner seals  71  are brought into pressure contact with the corresponding frame seals  102 . Hence, while the toner seals  71  and the frame seals  102  seal any gaps formed between the developing unit  7  and the corresponding toner cartridge  11 , the interior of the casing  51  of the toner cartridge  11  is in communication with the interior of the developing chamber  41  through the cartridge communication holes  58 . 
         [0132]    Only when the drawer unit  3  is accommodated in the main casing  2 , each main casing pressure member  20  presses the corresponding toner cartridge  11 . Accordingly, pressure of the toner cartridge  11  by the main casing pressure member  20  does not inhibit the operation guide unit  34  from shifting between the first posture and the second posture or the shutter  73  from moving between the open position and the closed position. In other words, when the drawer unit  3  is pulled outward from the main casing  2 , the toner cartridge  11  is not pressed by the main casing pressure member  20 . Thus, a force applied to the operation portion  36  when moving the operation guide unit  34  and the shutter  73  can be relatively small. As a result, excellent operability of the operation portion  36  can be further achieved. 
         [0133]    (5) Operation and Effect 5 
         [0134]    The drive force generation gear  62 , the first transmission gear  92 , the second transmission gear  93 , the third transmission gear  94  and the rack gear  45  constitute the drive mechanism (gear train) for moving the shutter  73  between the open position and the closed position. With this gear train, a force inputted into the operation portion  36  by its operation can be reliably transmitted to the shutter  73 . Hence, the shutter  73  can be reliably moved between the open position and the closed position. 
         [0135]    (6) Operation and Effect 6 
         [0136]    The toner cartridge  11  includes the guided portions  64  that are guided by the operation guide unit  34 . The guided portions  64  are fixed to the drive force generation gear  62 . In association with the shift of the operation guide unit  34  between the first posture and the second posture, the guided portions  64  are angularly moved so as to rotate the drive force generation gear  62 . Rotation of the drive force generation gear  62  generates a drive force to move the shutter  73 . That is, because the drive force generation gear  62  is integral with the guided portions  64 , a part of a force applied to the operation portion  36  to shift the operation guide unit  34  between the first posture and the second posture can be employed as a drive force to move the shutter  73 . Therefore, there is no need to provide a drive source (such as a motor) for generating a drive force for moving the shutter  73  independently from generating a force applied to the operation portion  36 . Accordingly, the structure of the color printer  1  can be simplified. 
         [0137]    (7) Operation and Effect 7 
         [0138]    The operation guide unit  34  rotates in association with operation of the operation portion  36 , so that the operation guide unit  34  can be shifted between the first posture and the second posture. Therefore, compared with a structure that the operation guide unit  34  is linearly operated to shift its posture, a necessary space for shifting the posture of the operation guide unit  34  can be reduced. Accordingly, the drawer unit  3  can be downsized. 
         [0139]    (8) Operation and Effect 8 
         [0140]    Since the main portion  35 , the operation portion  36 , and the guide portion  37  are integrally formed, the operation guide unit  34  can be reliably shifted between the first posture and the second posture when the operation portion  36  is operated. Further, compared with a structure that the main portion  35 , the operation portion  36 , and the guide portion  37  are separately formed, less parts and components are required to provide the operation guide unit  34 . Accordingly, the operation guide unit  34  can be downsized. 
         [0141]    (9) Operation and Effect 9 
         [0142]    The operation guide unit  34  includes the opposing portion  39  functioning as the retaining portion for retaining the toner cartridge  11  in the drawer unit  3  (for retaining the toner cartridge  11  in the developing unit  7 ). That is, the opposing portion  39  confronts the leading guided portion  64  of the toner cartridge  11  and positioned upstream of the leading guided portion  64  in the second direction when the operation guide unit  34  is in the second posture. Therefore, while the operation guide unit  34  is in the second posture, movement of the toner cartridge  11  toward a downstream side in the second direction can be restrained. As a result, the toner cartridge  11  can be prevented from being removed from the drawer frame  31  while the operation guide unit  34  is in the second posture. 
         [0143]    (10) Operation and Effect 10 
         [0144]    Further, the drawer unit  3  is provided with the pair of drawer unit pressure members  101  ( 101 L,  101 R) for pressing the toner cartridge  11  toward the developing unit  7 . Hence, when the toner cartridge  11  is mounted in the developing unit  7  in the first direction, the pair of drawer unit pressure members  101  presses the toner cartridge  11  toward the corresponding developing unit  7  with a suitable force. With this configuration, the toner cartridge  11  is temporarily fixed to the corresponding developing unit  7 . Thus, unintentional removal of the toner cartridge  11  from the drawer unit  3  can be prevented. Further, when the drawer unit  3  is moved, the pair of drawer unit pressure members  101  can prevent unwanted rattling of the toner cartridge  11 , thereby avoiding separation of the toner seal  71  from the frame seal  102  caused by the rattling. As a result, toner leakage from a portion between the toner seal  71  and the frame seal  102  can be restrained. 
         [0145]    (11) Operation and Effect 11 
         [0146]    The second direction is coincident with the pressing direction of the developing roller  9  toward the surface of the photosensitive drum  5 . This second direction is provided by the combination of the main casing pressure member  20 , the inclination of the guide groove  38 , and the guided portions  64 . Hence, any load directed in a direction crossing the second direction is not applied to the toner cartridge  11  during movement of the toner cartridge  11  toward and away from the photosensitive drum  5 . Accordingly, stable movement of the toner cartridge  11  can be realized when the developing roller  9  is pressed or separated relative to the photosensitive drum  5 . 
         [0147]    9. Modifications 
         [0148]    The toner cartridge  11  is not limited to the structure shown in  FIG. 6 . For example, a structure shown in  FIGS. 13 through 16  is also available. The toner cartridge  11  shown in  FIG. 6 , the left side surface  56  of the casing  51  is provided with the boss  61 , and the drive force generation gear  62  and the disk plate  63  are supported to the boss  61 . Instead of this structure, a toner cartridge  11 ′ has a base portion  111  that is formed in a generally rectangular-parallelepiped shape and rotatably supported to the boss  61 . The base portion  111  has a left side surface on which two guided portions  112  are provided. The two guided portions  112  are provided at positions in confrontation with each other, interposing the boss  61  therebetween. That is, the two guided portions  112  are spaced apart from each other at an angle of 180 degrees about the boss  61 . Each of the guided portions  112  has a columnar shape, and protrudes leftward from the left side surface of the base portion  111 . 
         [0149]    In the modification shown in  FIGS. 13 through 16 , instead of the operation guide unit  34  in the foregoing embodiment, an operation guide unit  34 ′ shown in  FIG. 14  is available. The operation guide unit  34 ′ has the main portion  35 , the operation portion  36  and the guide portion  37  formed with the guide groove  38  similar to the foregoing embodiment. The main portion  35  has a gear portion  113  along a part of an outer peripheral surface thereof. More specifically, the gear portion  113  and the guide portion  37  are provided at one side of the main portion  35 , and the operation portion  36  is provided at another side thereof. The gear portion  113  extends to cover the guide groove  38  like a peaked roof, and has an arcuate shape with a center angle of 90 degrees, and is arranged to extend along an outer circumferential surface of the guide portion  37 . The gear portion  113  has an outer circumferential surface provided with gear teeth  114 . Further, in the modification, a first transmission gear  92  in the above-described embodiment is not provided. That is, in this modification, the drive force transmission mechanism  91  only includes the second transmission gear  93  and the third transmission gear  94 . 
         [0150]    When the toner cartridge  11 ′ is not mounted in the space  12  formed in the drawer frame  31 , as shown in  FIG. 15 , the operation guide unit  34 ′ is in the first posture in which the guide groove  38  extends in the first direction (upper-to-lower direction) and the opposing portion  39  is positioned below the guide groove  38 . 
         [0151]    In the first posture, the gear portion  113  is disposed diagonally above and forward of the second transmission gear  93 , and the gear teeth  114  is not meshingly engaged with the second transmission gear  93 . 
         [0152]    When the toner cartridge  11 ′ is not mounted in the drawer unit  3 , the shutter  73  is in the closed position. Further, as shown in  FIG. 13 , the two guided portions  112  are aligned in the first direction. 
         [0153]    After the two guided portions  112  have been inserted into the guide groove  38  from above and the toner cartridge  11 ′ has been mounted in the space  12 , the user holds the operation portion  36  by his/her fingers to angularly rotate the operation guide unit  34 ′ in the counterclockwise direction in  FIG. 15 . Accordingly, the operation guide unit  34 ′ is shifted to the second posture as shown in  FIG. 16  from the first posture. 
         [0154]    In association with the shift of the operation guide unit  34 ′ to the second posture from the first posture, the guide groove  38  extends in the second direction that inclines diagonally downward and rearward. The opposing portion  39  is positioned upstream of the guided portions  112  in the second direction. Further, while the operation guide unit  34 ′ angularly rotates to shift its posture, the gear teeth  114  of the gear portion  113  is brought into meshedly engagement with the second transmission gear  93 . In association with the rotation of the operation guide unit  34 ′, a rotational force is transmitted to the second transmission gear  93  from the gear teeth  114 , and then to the third transmission gear  94  from the second transmission gear  93 . As a result, the third transmission gear  94  rotates in the counterclockwise direction in  FIG. 15 . In association with the rotation of the third transmission gear  94 , the shutter drive assembly  44  moves forward to a position forward of the openings  43  from a position opposing the openings  43 . In association with the movement of the shutter drive assembly  44 , the shutter  73  moves forward from the closed position along with the shutter drive assembly  44 . The shutter  73  is thus positioned at the open position. When the operation guide unit  34 ′ is in the second posture, the gear portion  113  is disposed diagonally above and rearward of the second transmission gear  93 . Further, meshing engagement of the gear teeth  114  with the second transmission gear  93  has been released before the operation guide unit  34 ′ is set to the second posture. 
         [0155]    When the operation guide unit  34 ′ is returned to the first posture from the second posture, the gear teeth  114  of the gear portion  113  is again brought into meshedly engagement with the second transmission gear  93  while the operation guide unit  34 ′ angularly rotates. In association with further angular rotation of the operation guide unit  34 ′, the shutter  73  is moved to the closed position from the open position by performing, in reverse order, the operation when the toner cartridge  11 ′ is mounted in the space  12 . 
         [0156]    Accordingly, the same operation and effect can be obtained even if the toner cartridge  11 ′ shown in  FIG. 13  and the operation guide unit  34 ′ shown in  FIG. 14  are adopted in place of the toner cartridge  11  shown in  FIG. 6  and the operation guide unit  34  shown in  FIG. 4 . 
         [0157]    In the above-described embodiment, the four operation guide units  34  are provided on the left side plate  32 . However, the operation guide units  34  may be provided both on the left side plate  32  and the right side plate  33 . In accordance therewith, the guided portions  64  may be provided both on the left side surface  56  and the right side surface  57  of the casing  51  of the toner cartridge  11 . 
         [0158]    In the above-described embodiment, mounting and dismounting direction (first direction) of the toner cartridge  11  is the same as the pressing direction provided by the main casing pressure member  20 . However, the pressing direction can be different from the mounting and dismounting direction. 
         [0159]    Further, the present invention may be applicable to a monochromatic laser printer instead of the color laser printer  1 . 
         [0160]    While the invention has been described in detail with reference to the embodiment thereof, it would be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention.