PATENT DOCUMENT

Abstract:
An image forming apparatus includes a casing, a photosensitive body, a toner accommodation component, a developing roller and an exposure unit configured to emit a laser beam toward the photosensitive body along an irradiating path. The image forming apparatus further includes a sheet feed roller configured to feed a sheet toward the photosensitive body. In some arrangements, the sheet feed roller is disposed at a position closer to the exposure unit than to the photosensitive body, and the developing device is disposed at a first height range relative to the bottom of the casing, the first height range being lower than the irradiation path. Moreover, the toner accommodation component is disposed at a second height range relative to the bottom of the casing, the second height range being higher than the irradiation path.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/056,159 filed Feb. 29, 2016, which is a continuation of U.S. patent application Ser. No. 14/458,394 filed Aug. 13, 2014, issued as U.S. Pat. No. 9,274,498 on Mar. 1, 2016, which claims priority from Japanese Patent Application Nos. 2013-168348 and 2013-168350, both filed on Aug. 13, 2013, the entire subject matters of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     Aspects of the present invention relate to an image forming apparatus which employs an electro-photographic method. 
     BACKGROUND 
     A related-art electro-photographic image forming apparatus includes a sheet feed cassette which accommodates recording sheets, a sheet feed roller which is disposed on the front upper side with respect to the sheet feed cassette, an image forming section which is disposed on the rear upper side with respect to the sheet feed roller, a laser scanner which is disposed on the rear upper side with respect to the image forming section, a fixing section which is disposed on the rear side with respect to the image forming section, and a sheet discharge section which is disposed on the upper side with respect to the fixing section (refer to JP-A-2005-17425). The image forming apparatus is configured to transport the recording sheet in a substantially S shape in an apparatus main body. 
     Incidentally, in recent years, from the viewpoint of a degree of freedom of an installation location or a storage location of an image forming apparatus, size-reduction of the image forming apparatus in a vertical direction is desired. However, in the image forming apparatus disclosed in JP-A-2005-17425, the laser scanner is disposed on the rear upper side with respect to the image forming section, and thus size-reduction in the vertical direction is restricted. 
     SUMMARY 
     Accordingly, an aspect of the present invention provides an image forming apparatus which can achieve size-reduction in a vertical direction. 
     According to an illustrative embodiment of the present invention, there is provided an image forming apparatus comprising a casing, a process unit, a cassette, a first roller, an exposure unit, a fixing unit and a second roller. The process unit is configured to be removably mounted to the casing, and is configured to form a developer image on a recording medium. The process unit includes a photosensitive body extending in a first direction which intersects a vertical direction. The cassette is disposed on a lower side in the vertical direction with respect to the process unit, and is configured to accommodate recording media to be supplied to the process unit. The first roller is disposed on one side in a second direction with respect to the process unit, and is configured to separate the recording media in the cassette one by one. The second direction is substantially perpendicular to the vertical direction and the first direction. The exposure unit is configured to expose the photosensitive body. The fixing unit is disposed on the other side in the second direction with respect to the process unit, and is configured to fix a developer image formed on a recording medium by the photosensitive body. The second roller is disposed on an upper side in the vertical direction with respect to the fixing unit and on the other side in the second direction with respect to the first roller, and is configured to transport the recording medium passed through the fixing unit to an outside of the casing. The casing includes a guide portion which is configured to guide the process unit into the casing. The exposure unit is disposed on the one side in the second direction with respect to the process unit and the guide portion. 
     According to this configuration, since the exposure unit is disposed on the one side in the second direction with respect to the process unit, the exposure unit and the process unit can be disposed so as to be arranged in the second direction. Therefore, it is possible to achieve size-reduction of the image forming apparatus in the vertical direction. 
     Further, the guide portion of the casing guides the removing and mounting of the process unit with respect to the casing. Therefore, it is possible to ensure smooth mounting and removing operations of the process unit even if the exposure unit and the process unit are disposed so as to be arranged in the second direction. 
     As a result, it is possible to achieve size-reduction of the image forming apparatus in the vertical direction and also to ensure smooth mounting and removing operations of the process unit. 
     According to another illustrative embodiment of the present invention, there is provided an image forming apparatus comprising a process unit, a cassette, a first roller, an exposure unit, a second roller and a transport guide. The process unit is configured to form a developer image on a recording medium, and includes a photosensitive body extending in a first direction which intersects a vertical direction. The cassette is disposed on a lower side in the vertical direction with respect to the process unit, and is configured to accommodate recording media. The first roller is disposed on one side in a second direction with respect to the process unit, and is configured to separate the recording media in the cassette one by one. The second direction is substantially perpendicular to the vertical direction and the first direction. The exposure unit is configured to expose the photosensitive body. The fixing unit is disposed on the other side in the second direction with respect to the process unit, and is configured to fix a developer image transferred on a recording medium from the photosensitive body. The second roller is disposed on an upper side in the vertical direction with respect to the fixing unit and on the other side in the second direction with respect to the first roller, and is configured to transport the recording medium passed through the fixing unit to an outside. The transport guide is configured to guide transport of a recording medium which is directed from the first roller toward the photosensitive body. The exposure unit is disposed on the one side in the second direction with respect to the photosensitive body. The exposure unit and the process unit are disposed to be arranged in the second direction along the transport guide. 
     According to this configuration, since the exposure unit is disposed on the one side in the second direction with respect to the process unit, and the exposure unit and the process unit are disposed to be arranged in the second direction along the transport guide, it is possible to achieve size-reduction of the image forming apparatus in the vertical direction. 
     According to the above-described image forming apparatus, it is possible to achieve size-reduction in the vertical direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects of the present invention will become more apparent and more readily appreciated from the following description of illustrative embodiments of the present invention taken in conjunction with the attached drawings, in which: 
         FIG. 1  is a center cross-sectional view showing a printer as an image forming apparatus according to a first illustrative embodiment of the present invention, and shows a state where a process cartridge is located at an internal position; 
         FIG. 2  is a center cross-sectional view of the printer shown in  FIG. 1 , and shows a state where the process cartridge is located at an extraction position; 
         FIG. 3  is a center cross-sectional view of the printer shown in  FIG. 1 , and shows a state where the process cartridge is located between the extraction position and an external position and a state where the process cartridge is located at the external position; 
         FIG. 4  is a plan view of the printer shown in  FIG. 1 , and shows a state where a cover body is removed; 
         FIG. 5  is a perspective view in which a drum cartridge shown in  FIG. 4  is viewed from an upper left side; 
         FIG. 6  is a center cross-sectional view of the drum cartridge shown in  FIG. 5 ; 
         FIG. 7A  is a center cross-sectional view of a developing cartridge shown in  FIG. 1 , and  FIG. 7B  is a left side view of the developing cartridge shown in  FIG. 7A ; 
         FIG. 8  is a center cross-sectional view showing a printer as an image forming apparatus according to a second illustrative embodiment of the present invention, and shows a state where a process cartridge is located at an internal position; 
         FIG. 9  is a center cross-sectional view of the printer shown in  FIG. 8 , and shows a state where the process cartridge is located at an extraction position; 
         FIG. 10  is a center cross-sectional view of the printer shown in  FIG. 8 , and shows a state where the process cartridge is located between the extraction position and an external position and a state where the process cartridge is located at the external position; 
         FIG. 11  is a plan view of the printer shown in  FIG. 8 , and shows a state where a cover body and a movable tray are removed; 
         FIG. 12  is a plan view of the printer shown in  FIG. 10 , and shows a state where the movable tray is located at a second position; 
         FIG. 13  is a center cross-sectional view showing a printer as an image forming apparatus according to a third illustrative embodiment of the present invention, and shows a state where a process cartridge is located at an internal position; 
         FIG. 14  is a center cross-sectional view of the printer shown in  FIG. 13 , and shows a state where a toner cartridge is removed from a main body casing; 
         FIG. 15  is a center cross-sectional view of the printer shown in  FIG. 13 , and shows a state where a process unit is located at an external position; 
         FIG. 16  is a center cross-sectional view of the process unit shown in  FIG. 15 ; 
         FIG. 17A  is a cross-sectional view taken along a line A-A of the process unit shown in  FIG. 16 , and  FIG. 17B  is a cross-sectional view taken along a line B-B of a toner cartridge shown in  FIG. 17A ; 
         FIG. 18A  is a plan view of the process unit shown in  FIG. 16 , and  FIG. 18B  is a cross-sectional view taken along a line C-C of the process unit shown in  FIG. 18A ; 
         FIG. 19  is an explanatory view showing a state where a process cartridge shown in  FIG. 18B  transports toner; 
         FIG. 20  is a center cross-sectional view showing a printer as an image forming apparatus according to a fourth illustrative embodiment of the present invention; 
         FIG. 21  is a center cross-sectional view showing a printer as an image forming apparatus according to a fifth illustrative embodiment of the present invention; 
         FIG. 22  is a center cross-sectional view showing a printer as an image forming apparatus according to a sixth illustrative embodiment of the present invention; and 
         FIG. 23A  is a center cross-sectional view of a process cartridge for a printer as an image forming apparatus according to a seventh illustrative embodiment of the present invention, and  FIG. 23B  is a center cross-sectional view of a drum cartridge for a printer as an image forming apparatus according to an eighth illustrative embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     1. Overall Configuration of Printer 
     As shown in  FIG. 1 , a printer  1  includes a main body casing  2 , a sheet feed section  3 , an image forming section  4 , a sheet discharge section  5 , a sheet guide section  6 , and a flat bed scanner  40 . 
     In the following description, when directions are mentioned, the right side of  FIG. 1  is referred to as the front side, and the left side of  FIG. 1  is referred to as the rear side, with a state of the printer  1  being horizontally placed as a reference. Further, with a state of the printer  1  being viewed from the front side as a reference of left and right sides, the front side of  FIG. 1  is referred to as the left side, and a back side of  FIG. 1  is referred to as the right side. For a process cartridge  15 , front and rear sides, left and right sides, and upper and lower sides are defined with a mounted state of the process cartridge  15  in a main body casing  2  (described later) as a reference. Specifically, directions in each drawing are indicated by arrows. 
     Incidentally, a left-right direction is an example of a first direction, the left side is one side of the first direction, and the right side is the other side of the first direction. Further, a front-rear direction is an example of a second direction, the front side is one side of the second direction, and the rear side is the other side of the second direction. Furthermore, an upper-lower direction is the same direction as a vertical direction, and the front-rear direction and the left-right direction are the same direction as a horizontal direction. 
     The main body casing  2  has a substantially box shape which extends in the left-right direction, and accommodates the sheet feed section  3 , the image forming section  4 , the sheet discharge section  5 , and the sheet guide section  6  in an inner space thereof. 
     The sheet feed section  3  supplies a sheet P to the image forming section  4 . The sheet feed section  3  is disposed at a lower part in the main body casing  2 . The sheet feed section  3  includes a sheet feed cassette  7  and a sheet feed roller  8 . 
     As shown in  FIGS. 1 and 3 , the sheet feed cassette  7  is disposed at a lower end in the main body casing  2 , and is removably mounted in the main body casing  2 . As shown in  FIG. 1 , the sheet feed cassette  7  has a substantially box shape which is opened upward, and accommodates a plurality of sheets P which are supplied to a process cartridge  15  (described later). Incidentally, although described later in detail, the sheet feed cassette  7  supports a sheet lift  10 , a sheet feed pad  11 , and a first pinch roller  12 . 
     The sheet feed roller  8  has a substantially columnar shape which extends in the left-right direction. The sheet feed roller  8  is disposed on the upper side with respect to a front end of the sheet feed cassette  7 , and is disposed further forward than the process cartridge  15 . 
     The image forming section  4  forms an image on the sheet P. The image forming section  4  is disposed on the upper side of the sheet feed section  3  in the main body casing  2 . The image forming section  4  includes the process cartridge  15 , a scanner unit  16 , and a fixing unit  17 . 
     Although described later in detail, as shown in  FIGS. 1 and 3 , the process cartridge  15  can be moved between an internal position where the process cartridge  15  lies in the main body casing  2  and an external position where the process cartridge  15  is removed from the main body casing  2 . As shown in  FIG. 1 , in a state of being located at the internal position, the process cartridge  15  is disposed at a substantially center in a side view in the main body casing  2 , and is disposed on the upper side with respect to a substantially center part of the sheet feed cassette  7  in the front-rear direction. That is, the sheet feed cassette  7  is disposed on the lower side with respect to the process cartridge  15 . 
     The process cartridge  15  includes a drum cartridge  18  and a developing cartridge  19 . 
     The drum cartridge  18  includes a photosensitive drum  20 , a transfer roller  21 , and a scorotron charger  22 . The photosensitive drum  20  is disposed at a rear end of the drum cartridge  18 . The transfer roller  21  is disposed on the lower side of the photosensitive drum  20 . An upper end of the transfer roller  21  is in contact with a lower end of the photosensitive drum  20 . The scorotron charger  22  is disposed with respect to the photosensitive drum  20  with a slight gap therebetween on the rear upper side of the photosensitive drum  20 . 
     As shown in  FIG. 7A , the developing cartridge  19  includes a developing roller  26 , a supply roller  27 , and a layer thickness regulation blade  28 , and accommodates toner. 
     The developing roller  26  has a substantially columnar shape extending in the left-right direction, and is disposed at a rear end of the developing cartridge  19 . An upper part and a rear part of the developing roller  26  are exposed from the developing cartridge  19  as shown in  FIG. 1 , and a rear upper end of the developing roller  26  is in contact with a front lower end of the photosensitive drum  20 . 
     As shown in  FIG. 7A , the supply roller  27  has a substantially columnar shape extending in the left-right direction, and is disposed on the front lower side with respect to the developing roller  26 . A rear upper end of the supply roller  27  is in pressing contact with a front lower end of the developing roller  26 . 
     The layer thickness regulation blade  28  is disposed on the front upper side of the developing roller  26 . The layer thickness regulation blade  28  has a plate shape extending in the upper-lower direction in a side view. Further, a lower end of the layer thickness regulation blade  28  is in contact with a front end of the developing roller  26 . 
     As shown in  FIG. 1 , the scanner unit  16  is disposed on the front side with respect to the process cartridge  15 , and is disposed on the upper side with respect to the sheet feed roller  8  with an interval therebetween. Specifically, the scanner unit  16  is disposed so as to overlap the process cartridge  15  and the fixing unit  17  when projected in the front-rear direction, and is disposed so as to overlap the sheet feed roller  8  when projected in the upper-lower direction. In addition, the scanner unit  16  is disposed in a direction which connects the front upper side to the rear lower side so as to be inclined downward toward the rear side. Further, the scanner unit  16  emits a laser beam L based on image data toward the photosensitive drum  20  as indicated by a solid line of  FIG. 1 . 
     The fixing unit  17  is disposed on the rear upper side with respect to the process cartridge  15  with an interval therebetween. That is, the fixing unit  17  is disposed further rearward than the process cartridge  15 . The fixing unit  17  includes a heating roller  30  and a pressing roller  31 . 
     The heating roller  30  is disposed on the rear upper side with respect to the scorotron charger  22  of the process cartridge  15  with an interval therebetween. The pressing roller  31  is disposed on the rear lower side with respect to the heating roller  30 . A front upper end of the pressing roller  31  is in pressing contact with a rear lower end of the heating roller  30 . 
     The sheet discharge section  5  is disposed on the upper side with respect to the fixing unit  17 . The sheet discharge section  5  includes a pair of guide rollers  33  and a pair of sheet discharge rollers  34 . 
     The pair of guide rollers  33  are disposed on the rear upper side with respect to the fixing unit  17  with an interval therebetween. Each of the pair of guide rollers  33  has a substantially columnar shape extending in the left-right direction, and the guide rollers  33  are in contact with each other in a direction which connects the front upper side to the rear lower side. 
     The pair of sheet discharge rollers  34  are disposed on the front upper side with respect to the fixing unit  17  with an interval therebetween, and is disposed further rearward than the photosensitive drum  20 . That is, the pair of sheet discharge rollers  34  are disposed further upward than the fixing unit  17 , and further rearward than the sheet feed roller  8 . Each of the pair of sheet discharge rollers  34  has a substantially columnar shape extending in the left-right direction, and the sheet discharge rollers  34  are in contact with each other in a direction which connects the front upper side to the rear lower side. 
     Although described later in detail, the sheet guide section  6  guides transport of the sheet P so that the sheet P is transported from the sheet feed cassette  7  by the sheet feed roller  8  to reach the sheet discharge rollers  34  through a contact point N between the photosensitive drum  20  and the transfer roller  21 . The sheet guide section  6  defines a transport path T in a substantially S shape in a side view. 
     The flat bed scanner  40  is disposed adjacent to the main body casing  2  on the upper side, and is disposed on the upper side with respect to a sheet discharge tray  35  (described later) with an interval therebetween. The flat bed scanner  40  includes a shaft portion  44 , a pressing cover  41 , a glass surface  42 , and a CCD sensor  43 . 
     The shaft portion  44  is provided at a rear lower end of the flat bed scanner  40 . The shaft portion  44  has a substantially columnar shape extending in the left-right direction, and is rotatably supported at a rear upper end of the main body casing  2 . Thus, the flat bed scanner  40  swings with respect to the main body casing  2  with the shaft portion  44  as a fulcrum. 
     The flat bed scanner  40  has a configuration in which an original document is placed between the pressing cover  41  and the glass surface  42 , and then image information of the original document is read by the CCD sensor  43 . 
     2. Details of Main Body Casing 
     As shown in  FIG. 3 , the main body casing  2  includes a pair of side walls  50 , a rear wall  51 , a front wall  52 , a bottom wall  53 , and a top wall  54 , which are integrally formed. 
     The pair of side walls  50  are respectively disposed at both left and right ends of the main body casing  2 , and are disposed with an interval therebetween in the left-right direction. Each of the pair of side walls  50  has a substantially L plate shape in a side view. Specifically, a rear part  63  of the side walls  50  has a substantially rectangular shape extending in the upper-lower direction in a side view. A front part  64  of the side walls  50  has a substantially rectangular shape extending in the front-rear direction in a side view, and extends forward from a lower part of a front edge of the rear part  63 . 
     Further, each of the pair of side walls  50  includes a groove  46 . 
     The grooves  46  are disposed on inner surfaces in the left-right direction of the front parts  64  of the respective side walls  50  so as to match each other when projected in the left-right direction. In the present illustrative embodiment, configurations of the grooves  46  are the same as each other in the pair of side walls  50 . Therefore, in the following description of the grooves  46 , the groove  46  disposed on the right side wall  50  will be described in detail, and description of the groove  46  disposed on the left side wall  50  will be omitted. 
     The groove  46  is recessed outward in the left-right direction on the inner surface in the left-right direction of the front part  64  of the side wall  50  and is opened upward. The groove  46  includes a first groove  47  and a second groove  56 . 
     The first groove  47  is located at an upper part of the groove  46 , and is disposed at an upper part on the inner surface in the left-right direction of the front part  64  of the side wall  50 . A front end of the first groove  47  is disposed with respect to the rear part of the scanner unit  16  with an interval therebetween in the left-right direction. 
     The first groove  47  has a substantially rectangular shape extending in the front-rear direction in a side view, and is recessed downward from an upper edge of the front part  64  of the side wall  50 . 
     The second groove  56  is a lower part of the groove  46 , and is connected to a rear lower end of the first groove  47  and extends toward the rear lower side. Thus, the second groove  56  is disposed further rearward than the scanner unit  16 . 
     The second groove  56  includes a large width portion  57  and a small width portion  58  which are integrally formed. 
     The large width portion  57  extends so as to be inclined rearward downward from the rear part at the lower edge of the first groove  47 . A width of the large width portion  57  is reduced toward the rear lower side. 
     The small width portion  58  is connected to the lower end of the large width portion  57  and extends toward the rear lower side. The small width portion  58  has a substantially arc shape with a center at a rotation shaft  78  (described later) when viewed from the left-right direction. A width of the small width portion  58  is approximately the same as an outer diameter of an end of a drum shaft  131  (described later) in the left-right direction. 
     The rear wall  51  is disposed at a rear end of the main body casing  2 . The rear wall  51  has a substantially rectangular shape extending in the left-right direction when viewed from the rear side. Each of both left and right ends of the rear wall  51  is connected to the rear end of the rear part  63  of each side wall  50 . 
     The front wall  52  is disposed at a front end of the main body casing  2 . The front wall  52  has a rectangular shape extending in the left-right direction when viewed from the front side. Each of both left and right ends of the front wall  52  is connected to the front end of the front part  64  of each side wall  50 . The front wall  52  includes a cassette opening  60  and a sheet opening  61 . 
     The cassette opening  60  is disposed at a lower end of the front wall  52 . The cassette opening  60  has a shape and a size which allow the sheet feed cassette  7  to pass through the cassette opening, and penetrates through the lower end of the front wall  52  in the front-rear direction. The cassette opening  60  allows the sheet feed cassette  7  to pass therethrough when the sheet feed cassette  7  is mounted to or removed from the main body casing  2 . 
     The sheet opening  61  is disposed on the upper side of the cassette opening  60  with an interval therebetween at the front wall  52 . The sheet opening  61  has a shape and a size which allow the sheet P to pass through the sheet opening  61 , and penetrates through a substantially vertical center part of the front wall  52  in the front-rear direction. Although described later in detail, the sheet opening  61  receives the sheet P which is supplied from outside of the main body casing  2 . 
     The bottom wall  53  is disposed at the lower end of the main body casing  2 . The bottom wall  53  has a substantially rectangular plate shape in a bottom view. Each of both left and right ends of the bottom wall  53  is connected to the lower end of each side wall  50 , and a rear end of the bottom wall  53  is connected to a lower end of the rear wall  51 . 
     The top wall  54  is disposed at an upper end of the main body casing  2 . The top wall  54  includes a flat bed support wall  65 , a tray wall  66 , and a mounting/removing guide wall  67 . 
     The flat bed support wall  65  is disposed on the upper side of the sheet discharge section  5 . The flat bed support wall  65  is connected to the upper end of the rear wall  51 , and extends forward and in the left-right direction. Both left and right ends of the flat bed support wall  65  are connected to the upper end of the rear part  63  of each side wall  50 . Further, the flat bed support wall  65  is in contact with a rear part of the flat bed scanner  40  from the lower side so as to support the flat bed scanner  40 . Further, a connecting part of the flat bed support wall  65  and the rear wall  51  rotatably supports the shaft portion  44  of the flat bed scanner  40 . 
     The tray wall  66  is bent from a front end of the flat bed support wall  65 , and extends downward and in the left-right direction. Both left and right ends of the tray wall  66  are connected to the upper part at the front end of the rear part  63  of each side wall  50 . The tray wall  66  includes a sheet discharge port  68 . 
     The sheet discharge port  68  is disposed at an upper end of the tray wall  66 , and is disposed on the front side of the pair of sheet discharge rollers  34 . The sheet discharge port  68  has a shape and a size which allow the sheet P to pass through the sheet discharge port  68 , and penetrates through the upper end of the tray wall  66  in the front-rear direction. 
     The mounting/removing guide wall  67  is disposed on the front side with respect to the tray wall  66  with an interval therebetween, and is disposed on the upper side of the scanner unit  16  so as to cover the scanner unit  16 . The mounting/removing guide wall  67  is connected to the upper end of the front wall  52  and extends rearward and in the left-right direction. Specifically, the mounting/removing guide wall  67  includes a curved wall  69 , an inclined wall  70 , a guide wall  71 , and a regulation wall  72  which are integrally formed. 
     The curved wall  69  is connected to the upper end of the front wall  52 , and extends so as to be curved rearward upward. Both left and right ends of the curved wall  69  are connected to the front upper end of the front part  64  of each side wall  50 . 
     The inclined wall  70  is connected to the upper end of the curved wall  69 , and extends so as to be inclined downward rearward. 
     The guide wall  71  is bent from a rear end of the inclined wall  70  so that a downward inclination thereof is larger than that of the inclined wall  70 , and extends so as to be inclined downward rearward. 
     The regulation wall  72  is bent from a rear end of the guide wall  71 , and protrudes downward. 
     In addition, the mounting/removing guide wall  67  includes cutout portions  73  as shown in  FIG. 4 . 
     The cutout portions  73  are respectively disposed at the left and right ends of the mounting/removing guide wall  67 , so as to correspond to a cover guide  80  (described later). The cutout portions  73  are cut out in a substantially rectangular shape in a plan view from left and right ends of the regulation wall  72  up to an approximately center of the inclined wall  70  in the front-rear direction. Thus, the cutout portions  73  communicate with the front end of the first groove  47  of the main body casing  2  in the upper-lower direction. 
     As shown in  FIG. 1 , a process opening  75  is defined by the regulation wall  72 , the lower end of the tray wall  66 , and the upper end of the front part  64  of each side wall  50  located between the regulation wall  72  and the tray wall  66 . That is, the main body casing  2  has the process opening  75 . 
     The process opening  75  has a substantially rectangular shape in a plan view, and allows the inner space of the main body casing  2  to communicate with the outside of the main body casing  2  in the upper-lower direction. The process opening  75  has a size which allows the process cartridge  15  to pass through the process opening  75 . 
     Further, the main body casing  2  includes a top cover  77  for opening and closing the process opening  75 . 
     The top cover  77  includes a rotation shaft  78 , a cover body  79 , and a cover guide  80 . 
     The rotation shaft  78  has a substantially columnar shape extending in the left-right direction, and is rotatably supported at the lower end of the tray wall  66 , that is, at a rear edge of the process opening  75 . 
     The cover body  79  has a plate shape, and extends outward in the radial direction of the rotation shaft  78  from the rotation shaft  78 . 
     The cover guide  80  is disposed at each of both left and right ends in a front part of a lower surface of the cover body  79 . Herein, when the left cover guide  80  and the right cover guide  80  are differentiated from each other, the left cover guide  80  is indicated by a left cover guide  80 L, and the right cover guide  80  is indicated by a right cover guide  80 R. 
     The cover guide  80  has a substantially L shape in a side view. A dimension of the cover guide  80  in the left-right direction is smaller than a dimension of the cutout portion  73  in the left-right direction as shown in  FIG. 4 . Further, the cover guide  80  includes a regulation portion  81  and a guide body  86  which are integrally formed as shown in  FIG. 1 . 
     The regulation portion  81  is connected to an approximately center part in the front-rear direction at an end of the cover body  79  in the left-right direction and extends toward the front lower side. 
     The guide body  86  is connected to a lower end of the regulation portion  81  and extends forward. Thus, the guide body  86  is substantially parallel to the cover body  79 , and extends so as to be separated from the rotation shaft  78 . Specifically, the guide body  86  includes an engagement portion  82 , a first cover guide  83 , a second cover guide  84 , and an introduction portion  85  which are integrally formed. 
     The engagement portion  82  is connected to the lower end of the regulation portion  81  and extends toward the front lower side, and is then bent so as to extend toward the front upper side. 
     The first cover guide  83  is bent from a front end of the engagement portion  82  so that a forward inclination is larger than that of a front part of the engagement portion  82 , and extends so as to be inclined slightly upward forward. 
     The second cover guide  84  is bent from a front end of the first cover guide  83 , and extends so as to be inclined slightly downward forward. 
     The introduction portion  85  is bent from a front end of the second cover guide  84 , and extends so as to be further inclined slightly downward forward than the second cover guide  84 . 
     The top cover  77  can swing between a closed position where the process opening  75  is closed and an open position where the process opening  75  is opened with the rotation shaft  78  as a fulcrum as shown in  FIG. 2 . 
     As shown in  FIG. 1 , in a state where the top cover  77  is located at the closed position, the cover body  79  is disposed so as to extend forward from the rotation shaft  78 , and a front end of the cover body  79  is adjacent to an upper side of the connection part of the curved wall  69  and the inclined wall  70 . In a state where the top cover  77  is located at the closed position, the front surface of the tray wall  66  and the upper surface of the cover body  79  configure the sheet discharge tray  35 . 
     Each of both left and right cover guides  80  is disposed inside the first groove  47  of the main body casing  2  via the cutout portion  73  in a state where the top cover  77  is located at the closed position as shown in  FIG. 4 . Thus, the left cover guide  80 L is disposed on the left with respect to the scanner unit  16  with an interval therebetween, and the right cover guide  80 R is disposed on the right side with respect to the scanner unit  16  with an interval therebetween. The introduction portion  85  of the guide body  86  overlaps the scanner unit  16  when projected in the left-right direction as shown in  FIG. 1 . 
     On the other hand, as shown in  FIG. 2 , in a state where the top cover  77  is located at the open position, the cover body  79  is disposed in a direction which connects the front upper side and the rear lower side, and the front end of the cover body  79  is disposed on the upper side with respect to the inclined wall  70  with an interval therebetween through which the process cartridge  15  can pass. 
     The first cover guide  83  of the cover guide  80  is disposed so as to be substantially parallel to the guide wall  71  of the mounting/removing guide wall  67 , and the second cover guide  84  is disposed so as to be substantially parallel to the inclined wall  70  of the mounting/removing guide wall  67 . 
     3. Details of Sheet Guide Section 
     The sheet guide section  6  is disposed in the main body casing  2  as shown in  FIG. 1 . The sheet guide section  6  includes a first sheet guide  88 , a second sheet guide  89 , a third sheet guide  90 , a fourth sheet guide  91 , and a fifth sheet guide  92 . 
     The first sheet guide  88  is a part which is located on the lower side of the scanner unit  16  in the sheet guide section  6 , and guides transport of the sheet P which is directed from the sheet feed cassette  7  toward the sheet feed roller  8  and is returned toward the rear upper side. The first sheet guide  88  includes an upstream part  94 , a middle part  95 , and a downstream part  96 . 
     The upstream part  94  is an upstream part in a transport direction of the sheet P in the first sheet guide  88 , and guides transport of the sheet P accommodated in the sheet feed cassette  7 , which is directed toward the sheet feed roller  8 . The upstream part  94  includes a pickup roller  9 , the sheet lift  10 , and the sheet feed pad  11 . 
     The pickup roller  9  has a substantially columnar shape extending in the left-right direction, and is disposed on the rear side of the sheet feed roller  8  with an interval therebetween. 
     The sheet lift  10  has a substantially rectangular plate shape in a plan view, and is disposed at a front part in the sheet feed cassette  7 . A front part of the sheet P accommodated in the sheet feed cassette  7  is placed on an upper surface of the sheet lift  10 . 
     The sheet lift  10  can swing with its rear end as a fulcrum, and is biased in a counterclockwise direction in a left side view at all times by a spring member (not shown). That is, a front end of the sheet lift  10  is biased toward the pickup roller  9  by the spring member (not shown). Therefore, the front end of the sheet P placed on the upper surface of the sheet lift  10  is interposed between the front end of the sheet lift  10  and the pickup roller  9 . 
     The sheet feed pad  11  is disposed on the front lower side of the pickup roller  9 , and is also disposed on the front lower side of the sheet feed roller  8 . The sheet feed pad  11  has a plate shape, and extends in a direction which connects the front upper side to the rear lower side in a side view. An upper surface of the sheet feed pad  11  is in contact with a front lower end of the sheet feed roller  8 . 
     The middle part  95  is a part which is disposed between the upstream part  94  and the downstream part  96  in the first sheet guide  88 , and guides transport of the sheet P which is returned by the sheet feed roller  8 . The middle part  95  includes a first pinch roller  12 , a second pinch roller  13 , a curved guide  97 , and a linear guide  98 . 
     The first pinch roller  12  is disposed on the front upper side with respect to the sheet feed pad  11 , and is also disposed on the front side of the sheet feed roller  8 . The first pinch roller  12  has a substantially columnar shape extending in the left-right direction, and a rear end of the first pinch roller  12  is in contact with the front end of the sheet feed roller  8 . 
     The second pinch roller  13  is disposed on the front upper side of the first pinch roller  12 , and is also disposed on the front side of the sheet feed roller  8  with an interval therebetween. The second pinch roller  13  has a substantially columnar shape extending in the left-right direction. 
     The curved guide  97  is disposed on the rear upper side of the second pinch roller  13 , and is disposed on the upper side with respect to the upper end of the sheet feed roller  8  with an interval therebetween. The curved guide  97  has a plate shape extending in the front-rear direction, and is curved toward the front upper side in a side view. 
     The linear guide  98  is disposed on the rear lower side of the curved guide  97  with an interval therebetween, and is disposed to be adjacent to the upper end of the sheet feed roller  8  on the rear side. The linear guide  98  has a plate shape extending in the front-rear direction. 
     The downstream part  96  is a downstream part in the transport direction of the sheet P in the first sheet guide  88 , and guides transport of the sheet P which is directed from the sheet feed roller  8  to the second sheet guide  89 . The downstream part  96  includes a pair of first transport rollers  100 , a pair of second transport rollers  101 , and a pair of inclined guides  99 . 
     The pair of first transport rollers  100  are disposed to be adjacent to the rear end of the linear guide  98  on the rear side, and is also disposed on the lower side of the scanner unit  16 . The pair of first transport rollers  100  are disposed further rearward than the sheet feed roller  8 . Each of the pair of first transport rollers  100  has a substantially columnar shape extending in the left-right direction, and the first transport rollers  100  are in contact with each other in the upper-lower direction. 
     The pair of second transport rollers  101  are disposed on the rear lower side with respect to the pair of first transport rollers  100  with an interval therebetween, and is disposed further rearward than the scanner unit  16 . Each of the pair of second transport rollers  101  has a substantially columnar shape extending in the left-right direction, and the second transport rollers  101  are in contact with each other in the upper-lower direction. 
     The pair of inclined guides  99  are disposed between the pair of first transport rollers  100  and the pair of second transport rollers  101 . The pair of inclined guides  99  are disposed on the lower side with respect to the rear part of the scanner unit  16 , and is disposed approximately along the inclination of the scanner unit  16 . Specifically, the pair of inclined guides  99  is inclined downward as proceeding downstream in the transport direction of the sheet P at the downstream part  96 . 
     Each of the pair of inclined guides  99  has a plate shape extending in a direction which connects the front upper side to the rear lower side in a side view, and the inclined guides  99  are disposed with an interval therebetween so as to allow the sheet P to pass therethrough in a direction which connects the front lower side and the rear upper side. 
     The second sheet guide  89  is a part which is disposed on the lower side of the process cartridge  15  in the sheet guide section  6 , and includes a guide part  107  and a reception part  105  which are integrally formed. 
     The guide part  107  is disposed on the lower side of the developing cartridge  19 , and guides transport of the sheet P which is directed from the first sheet guide  88  toward the contact point N between the photosensitive drum  20  and the transfer roller  21  along a sheet feed path  135  (described later). 
     The guide part  107  is disposed to be adjacent to the pair of second transport rollers  101  on the rear side so as to be connected to a downstream end of the first sheet guide  88  in the transport direction. The second sheet guide  89  extends in the front-rear direction in a side view. The second sheet guide  89  includes a guide protrusion  103 . 
     The guide protrusion  103  is disposed at a rear end of an upper surface of the guide part  107 , that is, a downstream end of the guide part  107  in the transport direction of the sheet P. The guide protrusion  103  corresponds to the sheet feed path  135  (described later), and is disposed on the front lower side of the sheet feed path  135 . The guide protrusion  103  has a substantially rectangular shape in a side view, and protrudes upward from the upper surface of the guide part  107 . 
     The reception part  105  is disposed on the lower side of a transfer accommodation wall  113  (described later), and is disposed to be adjacent to the guide part  107  on the rear side. The reception part  105  is connected to the rear end of the guide part  107  and extends rearward. Further, the reception part  105  includes a recess portion  104 . 
     The recess portion  104  is recessed from an upper surface of the reception part  105  toward the rear lower side. The recess portion  104  has a substantially curved shape in a side view, and is disposed along the rear end of the process cartridge  15 , specifically, a rear end of a roller accommodation portion  122  (described later). 
     The third sheet guide  90  is a part which is disposed between the process cartridge  15  and the fixing unit  17  in the sheet guide section  6 , and guides transport of the sheet P which passes through the contact point N between the photosensitive drum  20  and the transfer roller  21  and is then directed toward the fixing unit  17 . The third sheet guide  90  is connected to the rear end of the reception part  105 , and extends toward the rear upper side so as to be directed toward the fixing unit  17 . 
     The fourth sheet guide  91  is a part which is disposed between the pair of guide rollers  33  and the pair of sheet discharge rollers  34  in the sheet guide section  6 , and guides transport of the sheet P which passes through the pair of guide rollers  33  and is then returned to the pair of sheet discharge rollers  34 . The fourth sheet guide  91  is disposed on the lower side of the flat bed support wall  65 , and protrudes downward from the front part of the lower surface of the flat bed support wall  65 . The fourth sheet guide  91  includes a concave portion  106 . 
     The concave portion  106  has a substantially U shape which is opened toward the front lower side in a side view, and is recessed toward the rear upper side from the lower end of the fourth sheet guide  91 . A rear end of the concave portion  106  is disposed on the upper side of the pair of guide rollers  33 , and a front end of the concave portion  106  is disposed on the rear side of the pair of sheet discharge rollers  34 . 
     The fifth sheet guide  92  is disposed on the upper side of the middle part  95  of the first sheet guide  88  and the lower side of the front part of the scanner unit  16 , at the front end of the main body casing  2 . The fifth sheet guide  92  guides transport of the sheet P which is supplied from outside of the main body casing  2  via the sheet opening  61  and is directed toward the pair of first transport rollers  100 . The fifth sheet guide  92  includes an upper plate  108  and a lower plate  109 . 
     The upper plate  108  extends toward the rear lower side from an upper edge of the sheet opening  61  of the front wall  52  to the first transport rollers  100  on the upper side in a side view. A rear part of the upper plate  108  is disposed on the lower side with respect to the front part of the scanner unit  16 , and is disposed approximately along the inclination of the scanner unit  16 . Further, an inclination of the upper plate  108  is substantially the same as the inclination of the inclined guides  99 . That is, the scanner unit  16  is disposed approximately along the upper plate  108  of the fifth sheet guide  92  and the inclined guides  99  of the first sheet guide  88 . 
     The lower plate  109  extends rearward from a lower edge of the sheet opening  61  of the front wall  52 , is then bent so as to be substantially parallel to the upper plate  108 , and extends toward the rear lower side, in a side view. 
     A rear end of the lower plate  109  is connected to the rear end of the curved guide  97 . Thus, the fifth sheet guide  92  and the middle part  95  of the first sheet guide  88  are connected to each other on the front side of the pair of first transport rollers  100 . 
     4. Details of Process Cartridge 
     The process cartridge  15  includes the drum cartridge  18  and the developing cartridge  19  as described above. 
     (1) Drum Cartridge 
     The drum cartridge  18  includes a drum frame  23  as shown in  FIG. 5 . The drum frame  23  has a substantially rectangular frame shape extending in the left-right direction, and includes a pair of drum side walls  110 , a drum front wall  111 , a charger holding wall  112 , and a transfer accommodation wall  113  which are integrally formed. 
     The pair of drum side walls  110  are respectively disposed at both left and right ends of the drum frame  23 , and are disposed with an interval therebetween in the left-right direction. Each of the pair of drum side walls  110  has a substantially rectangular plate shape extending in the front-rear direction in a side view. Each of the pair of drum side walls  110  includes a first roller reception groove  118 , a second roller reception groove  119 , and a protrusion  134 . 
     The first roller reception groove  118  and the second roller reception groove  119  are disposed on an inner surface of each of the drum side walls  110  in the left-right direction. 
     The first roller reception groove  118 , as shown in  FIG. 6 , corresponds to a first roller  147  (described later), and is disposed at a rear part of the inner surface of the drum side wall  110  in the left-right direction. The first roller reception groove  118  is recessed outward in the left-right direction on the inner surface of the drum side wall  110  in the left-right direction, and extends so as to be inclined rearward downward from an upper edge of the drum side wall  110 . 
     The second roller reception groove  119  corresponds to a second roller  150  (described later), and is disposed on the front side of the first roller reception groove  118  with an interval therebetween on the inner surface of the drum side wall  110  in the left-right direction. The second roller reception groove  119  is recessed outward in the left-right direction on the inner surface of the drum side wall  110  in the left-right direction, and extends so as to be inclined rearward downward from an upper edge of the drum side wall  110 . 
     The protrusions  134  are respectively disposed on outer surfaces of the pair of drum side walls  110  in the left-right direction so as to correspond to the two cover guides  80 , as shown in  FIG. 5 . The protrusion  134  has a substantially triangular shape in a side view, and protrudes outward in the left-right direction from a front upper end of the outer surface of each drum side wall  110  in the left-right direction. 
     A front edge and a lower edge of the protrusion  134  have substantially the same as the shape of the engagement portion  82  of the cover guide  80  in a side view. Specifically, the upper edge of the protrusion  134  extends substantially in the front-rear direction; the front edge of the protrusion  134  extends from a front end of the upper edge of the protrusion  134  toward the rear lower side; and the lower edge of the protrusion  134  extends from a lower end of the front edge of the protrusion  134  toward the rear upper side and is connected to a rear end of the upper edge of the protrusion  134 . 
     The drum front wall  111  is disposed at the front end of the drum frame  23  as shown in  FIG. 6 . The drum front wall  111  has a substantially Z shape in a side view, and extends in the left-right direction. Each of both left and right ends of the drum front wall  111  is connected to the front end of each drum side wall  110 . 
     The drum front wall  111  includes a front wall body  114 , a handle portion  133 , and a contact portion  117  which are integrally formed. 
     The front wall body  114  has a plate shape extending in a direction which connects the front upper side to the rear lower side, and extends in the left-right direction. Each of both left and right ends of the front wall body  114  is connected to a part which is located slightly further rearward than the front edge of each drum side wall  110 . Thus, the front end of each drum side wall  110  is located further forward than the front wall body  114 . The front wall body  114  includes a laser passing hole  124 . 
     The laser passing hole  124  is disposed on an upper part of the front wall body  114  so as to correspond to a light path of the laser beam L. The laser passing hole  124  has a shape and a size which allow the laser beam L to pass through the laser passing hole  124 , and penetrates through the front wall body  114  in the front-rear direction. 
     The handle portion  133  has a plate shape extending from the upper end of the drum front wall  111  toward the rear lower side, and extends in the left-right direction as shown in  FIG. 5 . An upper surface of the handle portion  133  is substantially same level as an upper surface of each protrusion  134 . 
     The contact portion  117  has a plate shape which extends from the lower end of the drum front wall  111  toward the front upper side as shown in  FIG. 6 . 
     The charger holding wall  112  is disposed at a rear upper end of the drum frame  23 . The charger holding wall  112  has a substantially U shape which is opened toward the front lower side in a side view, and extends in the left-right direction. Each of both left and right ends of the charger holding wall  112  is connected to the rear upper end of each drum side wall  110 . 
     The transfer accommodation wall  113  is disposed at the rear lower end of the drum frame  23 , and is disposed on the lower side with respect to the charger holding wall  112  with an interval therebetween. The transfer accommodation wall  113  extends in the left-right direction, and is connected to the rear lower end of each drum side wall  110 . The transfer accommodation wall  113  includes a roller accommodation portion  122  and a lip portion  121  which are integrally formed. 
     The roller accommodation portion  122  is a rear part of the transfer accommodation wall  113 , and has a substantially U shape which is opened upward in a side view. The lip portion  121  is a front part of the transfer accommodation wall  113 , and extends so as to be inclined downward forward from an upper end of a front wall of the roller accommodation portion  122 . 
     An opening region between an upper end of a rear wall of the roller accommodation portion  122  and a lower end of a rear wall of the charger holding wall  112  is defined as a sheet discharge opening  136  for discharging the sheet P which has passed through the contact point N between the photosensitive drum  20  and the transfer roller  21 . 
     The drum cartridge  18  includes the photosensitive drum  20 , the transfer roller  21 , the scorotron charger  22 , and a handle  115 . 
     The photosensitive drum  20  is disposed between the rear ends of the pair of drum side walls  110 , and is disposed on the front lower side of the charger holding wall  112  and an upper side of the transfer accommodation wall  113 . The photosensitive drum  20  includes a drum body  132  and a drum shaft  131 . 
     The drum body  132  includes a cylindrical portion which has a substantially cylindrical shape extending in the left-right direction and is made of a metal, and a photosensitive layer which is coated over a circumferential surface of the cylindrical portion. 
     The drum shaft  131  has a substantially columnar shape extending in the left-right direction. A dimension of the drum shaft  131  in the left-right direction is larger than a dimension of the drum body  132  in the left-right direction, and is also larger than a dimension of the drum frame  23  in the left-right direction. The drum shaft  131  is disposed inside the drum body  132  so that a center axis line thereof matches a center axis line of the drum body  132 . 
     Further, the photosensitive drum  20  is rotatably supported at the drum frame  23  while both left and right ends of the drum shaft  131  are supported at the respective drum side walls  110 . Each of both left and right ends of the drum shaft  131  protrudes outward in the left-right direction from the drum side wall  110  as shown in  FIG. 5 . 
     The transfer roller  21  is disposed inside the roller accommodation portion  122  of the transfer accommodation wall  113  as shown in  FIG. 6 . The transfer roller  21  has a substantially columnar shape extending in the left-right direction. The transfer roller  21  is rotatably supported at the drum frame  23  while both left and right ends thereof are supported at the respective drum side walls  110 . The front upper end of the transfer roller  21  is in contact with the rear lower end of the drum body  132  of the photosensitive drum  20 . 
     The scorotron charger  22  is supported at the charger holding wall  112  inside the charger holding wall  112 . Thus, the scorotron charger  22  is disposed with respect to the photosensitive drum  20  on the rear upper side of the photosensitive drum  20  with a slight gap therebetween. 
     The handle  115  is disposed at the front end of the drum cartridge  18 , and is disposed on the front side with respect to the drum front wall  111 . Although described later in detail, the handle  115  swings between an accommodation position where the handle  115  stands up along the drum front wall  111  as shown in  FIGS. 1 and 4 to 6 , and an ejection position where a grip portion  129  (described later) is inclined so as to be separated forward from the drum front wall  111  as shown in  FIGS. 2 and 3 . Further, the following description will be made with a state where the handle  115  is located at the accommodation position shown in  FIGS. 1 and 4 to 6  as a reference. 
     As shown in  FIG. 5 , the handle  115  includes a handle body  125  and a swing shaft  126 . 
     The handle body  125  has a substantially U shape which is opened downward in a front view, and includes a pair of cylindrical portions  127 , a pair of connection portions  128 , and a grip portion  129  which are integrally formed. 
     The pair of cylindrical portions  127  are disposed with an interval therebetween in the left-right direction. Each of the pair of cylindrical portions  127  has a substantially cylindrical shape extending in the left-right direction. An inner diameter of the cylindrical portion  127  is slightly larger than an outer diameter of the swing shaft  126 . Each of the pair of connection portions  128  corresponds to each cylindrical portion  127  as shown in  FIG. 6 , is connected to the corresponding cylindrical portion  127 , and has a substantially rod shape extending toward the front upper side. The grip portion  129  is disposed between upper ends of the pair of connection portions  128 . The grip portion  129  has a substantially rod shape extending in the left-right direction, and both left and right ends thereof are connected to the upper ends of the respective connection portions  128 . 
     The swing shaft  126  has a substantially columnar shape extending in the left-right direction. The swing shaft  126  is inserted into the pair of cylindrical portions  127  so as to be relatively rotatable. 
     The handle  115  is supported at the drum frame  23  while both left and right ends of the swing shaft  126  are supported at the front lower ends of the pair of drum side walls  110 . 
     (2) Developing Cartridge 
     The developing cartridge  19  is removably mounted to the drum frame  23  as shown in  FIGS. 5 and 7B . 
     The developing cartridge  19  includes, as shown in  FIG. 7A , a developing frame  25 , the developing roller  26 , the supply roller  27 , the layer thickness regulation blade  28 , and an agitator  142 . 
     The developing frame  25  includes a pair of developing side walls  137 , a toner accommodation portion  139 , a blade support portion  138 , and a developing bottom wall  140  which are integrally formed. 
     The pair of developing side walls  137  are disposed at both left and right ends of the developing frame  25 , and are disposed with an interval therebetween in the left-right direction. Each of the pair of developing side walls  137  has a substantially rectangular plate shape extending in the front-rear direction in a side view as shown in  FIG. 7B . 
     The toner accommodation portion  139  is disposed between front parts of the pair of developing side walls  137  as shown in  FIG. 7A . The toner accommodation portion  139  has a substantially square tubular shape extending in the left-right direction, and both left and right ends thereof are closed by the front part of each developing side wall  137 . The toner accommodation portion  139  accommodates toner therein. The toner accommodation portion  139  includes a communication hole  141 . 
     The communication hole  141  is disposed at a lower end of a rear wall of the toner accommodation portion  139 , and penetrates through the rear wall of the toner accommodation portion  139  in the front-rear direction. 
     The blade support portion  138  is disposed at an upper end of a rear surface of a rear wall of the toner accommodation portion  139 . The blade support portion  138  has a substantially rectangular shape which protrudes rearward from the rear surface of the rear wall of the toner accommodation portion  139  in a side view. 
     The developing bottom wall  140  extends rearward from a lower end of the rear wall of the toner accommodation portion  139 . Both left and right ends of the developing bottom wall  140  are connected to lower ends of rear parts of the respective developing side walls  137 . The developing bottom wall  140  includes a front part  143  and a rear part  144  which are integrally formed. 
     The front part  143  has a substantially semicircular shape which is opened upward in a side view, and an inner circumferential surface of the front part  143  is curved along an outer circumferential surface of the supply roller  27 . A front end of the front part  143  is connected to a lower edge of the communication hole  141  of the rear wall of the toner accommodation portion  139 . The rear part  144  extends toward the rear upper side so as to be curved along an outer circumferential surface of the developing roller  26  from a rear end of the front part  143 . 
     The developing roller  26  is disposed on the front upper side of the rear part  144  of the developing bottom wall  140  with an interval therebetween. As shown in  FIGS. 7A and 7B , the developing roller  26  includes a roller body  145 , a developing roller shaft  146 , and the first roller  147 . 
     The roller body  145  is disposed between the rear ends of the pair of developing side walls  137 , and has a substantially cylindrical shape extending in the left-right direction. A dimension of the roller body  145  in the left-right direction is slightly smaller than an interval between the pair of developing side walls  137  in the left-right direction. 
     The developing roller shaft  146  has a substantially columnar shape extending in the left-right direction. A dimension of the developing roller shaft  146  in the left-right direction is larger than a dimension of the developing frame  25  in the left-right direction. The developing roller shaft  146  is fitted in the roller body  145  so that each of both left and right ends protrudes further outward than the roller body  145  in the left-right direction. Both left and right ends of the developing roller shaft  146  are rotatably supported at the developing side walls  137 . Thus, the developing roller  26  is rotatably supported at the developing frame  25 . Further, each of both left and right ends of the developing roller shaft  146  protrudes outward in the left-right direction from the developing side wall  137 . 
     Two first rollers  147  are provided so as to respectively correspond to both left and right ends of the developing roller shaft  146 . Each first roller  147  is disposed outward in the left-right direction with respect to the developing side wall  137 . The first roller  147  has a cylindrical shape extending in the left-right direction, and an inner diameter of the first roller  147  is substantially the same as an outer diameter of the developing roller shaft  146 . The first roller  147  is fitted in a part which is an end of the developing roller shaft  146  in the left-right direction and is located further outward than the developing side wall  137  in the left-right direction. 
     The supply roller  27  is disposed inside the front part  143  of the developing bottom wall  140 , and is disposed on the rear side of the communication hole  141  of the toner accommodation portion  139 . A rear upper end of the supply roller  27  is in contact with a front lower end of the roller body  145 . Further, the supply roller  27  is rotatably supported at the developing frame  25  while both left and right ends thereof are supported at the respective developing side walls  137 . 
     The layer thickness regulation blade  28  is fixed to a rear surface of the blade support portion  138 . A lower end of the layer thickness regulation blade  28  is in contact with a front end of the roller body  145 . 
     The agitator  142  is disposed at a rear lower end inside the toner accommodation portion  139 . The agitator  142  includes an agitator shaft  148 , and an agitator blade  149 . 
     The agitator shaft  148  has a substantially columnar shape extending in the left-right direction. A dimension of the agitator shaft  148  in the left-right direction is larger than a dimension of the developing frame  25  in the left-right direction. Both left and right ends of the agitator shaft  148  are rotatably supported at the respective developing side walls  137 . Thus, the agitator  142  is rotatably supported at the developing frame  25 . Further, each of both left and right ends of the agitator shaft  148  protrudes outward in the left-right direction from the developing side wall  137 . 
     The agitator blade  149  is made of a flexible film material. The agitator blade  149  extends outward in the radial direction of the agitator shaft  148  from a part where the agitator shaft  148  is located inside the toner accommodation portion  139 . 
     Two second rollers  150  are provided so as to respectively correspond to both left and right ends of the agitator shaft  148 . Each second roller  150  is disposed outward in the left-right direction with respect to the developing side wall  137 . The second roller  150  has a cylindrical shape extending in the left-right direction, and an inner diameter of the second roller  150  is substantially the same as an outer diameter of the agitator shaft  148 . The second roller  150  is fitted in a part which is an end of the agitator shaft  148  in the left-right direction and is located further outward in the left-right direction than the developing side wall  137 . 
     This developing cartridge  19  is mounted to the drum frame  23  shown in  FIG. 5  from the upper side, for example, by an operator. Specifically, the developing cartridge  19  is mounted to the drum frame  23  so that each first roller  147  is inserted into the corresponding first roller reception groove  118  from the upper side, and each second roller  150  is inserted into the corresponding second roller reception groove  119  from the upper side. 
     Accordingly, the developing cartridge  19  is mounted to the drum frame  23 , so as to configure the process cartridge  15 . 
     In a state where the developing cartridge  19  is mounted to the drum frame  23 , as shown in  FIG. 1 , the developing roller  26  is disposed on the front lower side of the photosensitive drum  20 , and the rear upper end of the roller body  145  is in contact with the front lower end of the drum body  132 . The rear part  144  of the developing bottom wall  140  is disposed on the front upper side with respect to the lip portion  121  of the transfer accommodation wall  113  with an interval therebetween. Thus, the rear part  144  of the developing bottom wall  140  and the lip portion  121  of the transfer accommodation wall  113  define the sheet feed path  135  for supplying the sheet P to the contact point N between the photosensitive drum  20  and the transfer roller  21 . 
     5. Removing and Mounting Operations of Process Cartridge with Respect to Main Body Casing 
     Next, a removing operation and a mounting operation of the process cartridge  15  with respect to the main body casing  2  will be described. 
     (1) Removing Operation of Process Cartridge from Main Body Casing 
     First, a description will be made of a removing operation of the process cartridge  15  from the main body casing  2 , that is, a movement of the process cartridge  15  from the internal position to the external position. 
     As shown in  FIG. 1 , in a state where the process cartridge  15  is located at the internal position, the rear end of the roller accommodation portion  122  of the drum cartridge  18  is disposed inside the recess portion  104  of the reception part  105 , and the left and right ends of the drum shaft  131  are inserted into the lower end of the small width portion  58  of the second groove  56 . In the state where the process cartridge  15  is located at the internal position, the protrusion  134  of the drum cartridge  18  is fitted in the engagement portion  82  of the cover guide  80 , and the front surface of the grip portion  129  of the handle  115  is in contact with the rear surface of the regulation wall  72  of the mounting/removing guide wall  67 . Thus, the handle  115  is located at the accommodation position where the connection portion  128  extends toward the front upper side from the swing shaft  126 , and the grip portion  129  is disposed on the upper side with respect to the swing shaft  126  in the main body casing  2 . 
     In order to move the process cartridge  15  from the internal position to the external position, as shown in  FIG. 2 , the operator swings the flat bed scanner  40  in the counterclockwise direction in a left side view, and also moves the top cover  77  from the closed position to the open position. Incidentally, the movement of the top cover  77  between the closed position and the open position may be interlocked with swing of the flat bed scanner  40  by using a known interlocking mechanism. 
     At this time, since the protrusion  134  is fitted in the engagement portion  82 , the protrusion  134  is moved toward the rear upper side according to a movement of the top cover  77  from the closed position to the open position. Accordingly, the process cartridge  15  is moved toward the front upper side and rotated in the counterclockwise direction in a left side view about the drum shaft  131  while the left and right ends of the drum shaft  131  are guided by the small width portion  58 . 
     Thus, the process cartridge  15  is located on the upper side with respect to the internal position, and the front upper end of the process cartridge  15  is located at the extraction position which lies outside the main body casing  2 , via the process opening  75 . That is, the small width portion  58  of the second groove  56  guides a movement of the process cartridge  15  from the internal position to the extraction position. 
     At this time, the handle  115  is inclined so as to be separated forward from the drum front wall  111  with the swing shaft  126  as a fulcrum by the gravity due to release of contact between the grip portion  129  and the regulation wall  72 , and swings from the accommodation position to the ejection position. In a state where the handle  115  is located at the ejection position, the grip portion  129  is located further downstream (upstream in a mounting direction X which is a direction from the front upper side toward the rear lower side) in a removing direction Y which is a direction from the rear lower side toward the front upper side than when the handle  115  is located at the accommodation position, and is located on the upper side of the connection part between the inclined wall  70  and the guide wall  71 , outside the main body casing  2 . The removing direction Y and the mounting direction X are directions intersecting the left-right direction. 
     That is, the process cartridge  15  is taken out from the internal position to the extraction position in interlocking with the movement of the top cover  77  from the closed position to the open position, and the handle  115  is moved from the accommodation position to the ejection position in interlocking with the movement of the process cartridge  15  from the internal position to the extraction position. 
     In a state where the top cover  77  is located at the open position, the guide body  86  of the cover guide  80  extends downstream (upstream in the mounting direction X) in the removing direction Y from the lower end of the regulation portion  81 . 
     In other words, the handle  115  and the guide body  86  of the cover guide  80  are disposed further upstream in the mounting direction X than the rotation shaft  78 . 
     Next, the operator, as shown in  FIGS. 2 and 3 , holds the grip portion  129  of the handle  115  located at the ejection position, and pulls out the process cartridge  15  toward the front upper side. 
     Accordingly, the protrusion  134  is moved toward the front upper side so as to be separated from the engagement portion  82  of the guide body  86 , and is thus moved onto the first cover guide  83 . The left-right ends of the drum shaft  131  are moved toward the front upper side, and are moved from the small width portion  58  to the large width portion  57 . Further, the first cover guide  83  guides a movement of the protrusion  134 , and the lower edge of the large width portion  57  guides a movement of the left-right ends of the drum shaft  131 . Thus, the process cartridge  15  is moved toward the front upper side in the removing direction Y while each of the front upper end and the rear end thereof are guided. 
     Then, the front end of the process cartridge  15 , specifically, the contact portion  117  of the drum front wall  111  is brought into contact with the regulation wall  72  of the mounting/removing guide wall  67 . 
     Next, when the operator pulls out the grip portion  129  of the handle  115  further toward the front upper side, the protrusion  134  is moved toward the front upper side, and is moved from on the first cover guide  83  to on the second cover guide  84 . The contact portion  117  is moved toward the front upper side so as to reach the guide wall  71 , and is slid on the guide wall  71 . At this time, the second cover guide  84  guides a movement of the protrusion  134 , and the guide wall  71  guides a movement of the contact portion  117 . 
     Thus, the process cartridge  15  is guided further toward the front upper side in the removing direction Y. 
     Successively, as shown in  FIG. 3 , when the operator pulls out the grip portion  129  of the handle  115  still further forward, the protrusion  134  is moved forward so as to be moved from on the second cover guide  84  to on the introduction portion  85 , and is then separated from the cover guide  80 . 
     At this time, the transfer accommodation wall  113  of the drum frame  23  sequentially reaches the upper side of the guide wall  71  and the inclined wall  70 , and is slid on the guide wall  71  and the inclined wall  70 . That is, each of the guide wall  71  and the inclined wall  70  guides a movement of the transfer accommodation wall  113 . Thus, the rear end of the process cartridge  15  is guided so that the process cartridge  15  is moved forward in the removing direction Y and is removed from the main body casing  2 . 
     Accordingly, the process cartridge  15  is moved from the internal position to the extraction position so as to be then moved from the extraction position downstream (upstream in the mounting direction X) in the removing direction Y and to reach the external position. 
     That is, the cover guide  80  and the mounting/removing guide wall  67  guide the movement of the process cartridge  15  from the extraction position to the external position. 
     Successively, the operator moves the top cover  77  from the open position to the closed position, and swings the flat bed scanner  40  in the clockwise direction in a left side view until the flat bed scanner  40  is brought into contact with the flat bed support wall  65 . 
     In the above-described manner, the removing operation of the process cartridge  15  from the main body casing  2  is completed. 
     (2) Mounting Operation of Process Cartridge to Main Body Casing 
     In order to mount the process cartridge  15  to the main body casing  2 , procedures are performed in a reverse order to the above-described removing operation. 
     Specifically, as shown in  FIG. 3 , the operator swings the flat bed scanner  40  in the counterclockwise direction in a left side view, and moves the top cover  77  from the closed position to the open position. 
     Next, the operator holds the handle portion  133  of the drum cartridge  18  and inserts the process cartridge  15  into the main body casing  2  toward the rear lower side through the process opening  75 . At this time, the protrusion  134  is located on the introduction portion  85  of the cover guide  80 , and the left and right ends of the drum shaft  131  are received by the large width portion  57  of the second groove  56 . 
     Successively, the operator holds the grip portion  129  of the handle  115 , and pushes the process cartridge  15  into the main body casing  2  toward the rear lower side. Therefore, the protrusion  134  reaches the upper side of the first cover guide  83  from the introduction portion  85  via the second cover guide  84 , and the left-right ends of the drum shaft  131  reach the continuous part of the large width portion  57  and the second groove  56  along the lower edge of the large width portion  57  of the second groove  56 . Thus, the drum cartridge  18  is moved toward the rear lower side in the mounting direction X so as to pass over the inclined wall  70  and the guide wall  71  of the mounting/removing guide wall  67 . 
     As shown in  FIG. 2 , if the process cartridge  15  is moved further toward the rear lower side, the protrusion  134  reaches the engagement portion  82  so as to be fitted therein, and the rear end of the protrusion  134  is also brought into contact with the regulation portion  81 . Further, the left and right ends of the drum shaft  131  reach the continuous part of the large width portion  57  and the small width portion  58 . 
     In the above-described manner, the movement of the drum cartridge  18  from the external position to the extraction position is completed. 
     That is, the cover guide  80  guides the movement of the process cartridge  15  from the external position to the extraction position. 
     Next, the operator moves the top cover  77  from the open position to the closed position, and also swings the flat bed scanner  40  in the clockwise direction in a left side view. 
     At this time, the protrusion  134  is moved toward the rear lower side due to the movement of the top cover  77 . Accordingly, the process cartridge  15  is moved toward the rear lower side and rotated in the clockwise direction about the drum shaft  131  in a left side view while the left and right ends of the drum shaft  131  are guided by the small width portion  58 . Thus, the process cartridge  15  is moved from the extraction position to the internal position as shown in  FIG. 1 . That is, the small width portion  58  of the second groove  56  guides the movement of the process cartridge  15  from the extraction position to the internal position. 
     When the process cartridge  15  is moved from the extraction position to the internal position, the grip portion  129  of the handle  115  is slid on the upper surface of the guide wall  71  of the mounting/removing guide wall  67  as shown in  FIG. 2 . Thus, the handle  115  is rotated in the counterclockwise direction in a left side view with the swing shaft  126  as a fulcrum so that the grip portion  129  becomes close to the drum front wall  111  from the ejection position. 
     Further, when the process cartridge  15  reaches the internal position, the handle  115  is located at the accommodation position while the grip portion  129  is disposed to be adjacent to the regulation wall  72  of the mounting/removing guide wall  67  on the rear side. 
     That is, the process cartridge  15  is moved from the extraction position to the internal position in interlocking with the movement of the top cover  77  from the open position to the closed position, and the handle  115  is moved from the ejection position to the accommodation position in interlocking with the movement of the process cartridge  15  from the extraction position to the internal position. 
     In the above-described manner, the mounting operation of the process cartridge  15  to the main body casing  2  is completed. 
     In the state where the process cartridge  15  is located at the internal position, the process cartridge  15  is disposed on the rear side of the scanner unit  16 , and is disposed on the upper side with respect to the second sheet guide  89  with a slight interval therebetween. The toner accommodation portion  139 , the supply roller  27 , the developing roller  26 , and the photosensitive drum  20  are sequentially disposed along the second sheet guide  89  from the front side to the rear side. 
     That is, in the state where the process cartridge  15  is located at the internal position, the scanner unit  16 , the toner accommodation portion  139 , the supply roller  27 , the developing roller  26 , and the photosensitive drum  20  are disposed so as to be sequentially arranged in the front-rear direction from the front side to the rear side. 
     Further, in the state where the process cartridge  15  is located at the internal position, the contact point N between the drum body  132  of the photosensitive drum  20  and the transfer roller  21  is located on the upper side with respect to the rear end of the second sheet guide  89 , and is thus located on the rear upper side with respect to the guide protrusion  103  of the second sheet guide  89 . 
     6. Image Forming Operation 
     (1) Developing Operation 
     The printer  1  starts an image forming operation under the control of a controller (not shown). When the image forming operation is started, the scorotron charger  22  uniformly charges the surface of the photosensitive drum  20 . 
     Then, the scanner unit  16  emits a laser beam L toward the surface of the photosensitive drum  20  in the rear lower direction. The laser beam L passes under the grip portion  129  of the handle  115 , then passes through the laser passing hole  124  of the drum front wall  111 , further pass over the developing cartridge  19 , and exposes the front circumferential surface of the drum body  132  of the photosensitive drum  20 . Thus, an electrostatic latent image based on image data is formed on the circumferential surface of the drum body  132 . Incidentally, the image data may include, for example, image data which is transmitted to the printer  1  from a personal computer (not shown) connected to the printer  1 , or image data read by the flat bed scanner  40 . 
     Further, the agitator  142  agitates toner in the toner accommodation portion  139  and supplies the agitated toner to the supply roller  27  via the communication hole  141 . The supply roller  27  supplies the toner which is supplied from the agitator  142 , to the developing roller  26 . At this time, the toner is positively friction-charged between the developing roller  26  and the supply roller  27  and is carried on the developing roller  26 . The layer thickness regulation blade  28  regulates the toner carried on the developing roller  26  to a constant thickness. 
     The developing roller  26  supplies the toner which is carried in the constant thickness to the electrostatic latent image on the circumferential surface of the drum body  132 . Thus, the toner image is carried on the circumferential surface of the drum body  132 . 
     (2) Sheet Feed Operation 
     A plurality of sheets P accommodated in the sheet feed cassette  7  are guided to the upstream part  94  and the middle part  95  of the first sheet guide  88 , and are moved toward the pair of first transport rollers  100 . Specifically, the sheet lift  10  swings in the counterclockwise direction in a left side view with a rear end as a fulcrum, and pinches front ends of the sheets P placed on the upper surface of the sheet lift  10  together with the pickup roller  9 . 
     The pickup roller  9  is rotated, and thus the sheets P are sent toward the sheet feed roller  8 . The sheet feed pad  11  guides the ends of the sent sheets P downstream in the transport direction so as to direct the ends thereof toward a gap between the sheet feed roller  8  and the sheet feed pad  11 . 
     Next, the sheet feed roller  8  is rotated, and thus the sheets P which reach between the sheet feed roller  8  and the sheet feed pad  11  are separated one by one. One sheet P separated by the sheet feed roller  8  passes between the sheet feed roller  8  and the first pinch roller  12  so as to be then sequentially guided to the second pinch roller  13  and the curved guide  97 , and are transported so as to be returned toward the rear upper side. 
     Next, the sheet P is guided to the upper surface of the linear guide  98  so as to reach between the pair of first transport rollers  100 . 
     On the other hand, a sheet P which is supplied from outside of the main body casing  2  is inserted into the main body casing  2  via the sheet opening  61  by an operator. The sheet P is guided to the lower plate  109  and the upper plate  108  of the fifth sheet guide  92  so as to reach between the pair of first transport rollers  100 . 
     The pair of first transport rollers  100  sends the sheet P to an interval between the pair of inclined guides  99  so as to transport the sheet P toward a gap between the pair of second transport rollers  101 . The pair of inclined guides  99  guides a movement of the sheet P which is directed toward the rear lower side. Thus, the sheet P reaches between the pair of second transport rollers  101 . 
     Successively, the pair of second transport rollers  101  sends the sheet P to a gap between the process cartridge  15  located at the internal position and the second sheet guide  89  so that the sheet P is transported toward the contact point N between the photosensitive drum  20  and the transfer roller  21 . Accordingly, the sheet P is moved rearward along the upper surface of the second sheet guide  89 . 
     Then, a leading end of the sheet P in the transport direction comes into contact with the guide protrusion  103 . Thus, the transport direction of the sheet P is changed so as to be directed toward the rear upper side, and the sheet P is supplied to the sheet feed path  135  of the process cartridge  15 . 
     The sheet P supplied to the sheet feed path  135  is transported toward the contact point N between the drum body  132  and the transfer roller  21  so as to pass through the contact point N. At this time, the transfer roller  21  transfers a toner image onto the sheet P from the photosensitive drum  20  so as to form the toner image on the sheet P. 
     The sheet P on which the toner image is formed is discharged through the sheet discharge opening  136  of the process cartridge  15 , and is guided by the third sheet guide  90  so as to be moved toward the fixing unit  17 . The sheet P passes between the heating roller  30  and the pressing roller  31 . At this time, the heating roller  30  and the pressing roller  31  heat and press the sheet P so that the toner image is thermally fixed to the sheet P. 
     The sheet P to which the toner image is fixed passes through the pair of guide rollers  33  so as to be guided to the concave portion  106  of the fourth sheet guide  91 , and is transported so as to be returned toward the front lower side and to reach between the pair of sheet discharge rollers  34 . 
     The pair of sheet discharge rollers  34  are rotated, and thus the sheet P is discharged on the sheet discharge tray  35  through the sheet discharge port  68 . The sheet P on which the toner image is formed and which is discharged from the main body casing  2  is placed on the sheet discharge tray  35 . 
     As described above, the sheet P accommodated in the sheet feed cassette  7  is transported along the transport path T with a substantially S shape in a side view, which is defined by the sheet guide section  6 . 
     7. Operations and Effects 
     (1) In the printer  1 , as shown in  FIG. 1 , the scanner unit  16  is disposed further forward than the process cartridge  15 . Therefore, the scanner unit  16  and the process cartridge  15  can be disposed so as to be arranged in the front-rear direction. Specifically, the scanner unit  16  and the process cartridge  15  are disposed to be arranged in the front-rear direction along the sheet guide section  6 . As a result, the printer  1  can be size-reduced in the vertical direction. 
     Further, as shown in  FIG. 3 , the small width portion  58  of the groove  46  of the main body casing  2  guides mounting and removing of the process cartridge  15  with respect to the main body casing  2 . Therefore, even if the scanner unit  16  and the process cartridge  15  are disposed so as to be arranged in the front-rear direction, smooth mounting and removing operations of the process cartridge  15  can be ensured. 
     Therefore, it is possible to achieve size-reduction of the printer  1  in the vertical direction and also to ensure smooth mounting and removing operations of the process cartridge  15 . 
     Further, in the printer  1 , when an image forming operation is performed, the sheet P is transported in a substantially S shape in a side view. Therefore, the sheet feed roller  8  is disposed further forward than the photosensitive drum  20 , and the fixing unit  17  is disposed further rearward than the photosensitive drum  20 . That is, the sheet feed roller  8 , the photosensitive drum  20 , and the fixing unit  17  are disposed so as to be approximately arranged in the front-rear direction. 
     In contrast, in a case where the scanner unit  16  is disposed further forward than the process cartridge  15 , and, when an image forming operation is performed, the sheet P is transported in a substantially C shape, the sheet feed roller  8 , the photosensitive drum  20 , and the fixing unit  17  are disposed so as to be approximately arranged in the vertical direction. Therefore, size-reduction of such a printer in the vertical direction is restricted. 
     On the other hand, since the sheet feed roller  8 , the photosensitive drum  20 , and the fixing unit  17  are disposed so as to be approximately arranged in the front-rear direction in the printer  1 , size-reduction in the vertical direction can be reliably achieved. Particularly, a dimension of the printer  1  in the horizontal direction depends on a size of a sheet P which can be accommodated in the sheet feed cassette  7 . Therefore, if the scanner unit  16 , the process cartridge  15 , and the fixing unit  17  are disposed so as to overlap the sheet feed cassette  7  when projected in the vertical direction, it is possible to prevent a size of the printer  1  in the horizontal direction from being increased. 
     That is, according to the printer  1 , it is possible to prevent a size in the horizontal direction from being increased and also to reliably achieve size-reduction in the vertical direction. 
     (2) Further, the main body casing  2  includes the sheet guide section  6  which guides transport of the sheet P as shown in  FIG. 1 . Further, the sheet guide section  6  guides transport of the sheet P which is directed toward the photosensitive drum  20  from the sheet feed roller  8 , and thus it is possible to reliably transport the sheet P from the sheet feed cassette  7  to the photosensitive drum  20 . 
     Further, the downstream part  96  of the first sheet guide  88  is inclined downward rearward. Therefore, the sheet P can be transported lowered as proceeding toward a downstream in the transport direction. As a result, in the printer  1 , the photosensitive drum  20  can be located on the further lower side, and thus the process cartridge  15  can be located on the further lower side. Therefore, it is possible to more reliably achieve size-reduction of the printer  1  in the vertical direction. 
     (3) Further, the sheet guide section  6  includes the guide part  107  of the second sheet guide  89  as shown in  FIG. 1 . Therefore, when an image forming operation is performed, the sheet P can be made to pass under the process cartridge  15  and then to reach the contact point N between the photosensitive drum  20  and the transfer roller  21 . 
     As a result, the process cartridge  15  can be located on the further lower side, and the sheet P can be made to reliably reach the photosensitive drum  20 . 
     Further, the contact point N between the photosensitive drum  20  and the transfer roller  21  is located at the rear end of the guide part  107 , more specifically, on the upper side with respect to the guide protrusion  103 . Therefore, the sheet P is guided to the guide part  107 , and is then transported toward the contact point N between the photosensitive drum  20  and the transfer roller  21  in the rear upper direction. Therefore, the sheet P which has passed between the photosensitive drum  20  and the transfer roller  21  can be smoothly transported toward the fixing unit  17  and the sheet discharge rollers  34 . 
     Further, the transfer roller  21  transfers a toner image onto the sheet P from the photosensitive drum  20  when the sheet P passes between the photosensitive drum  20  and the transfer roller  21 . Therefore, it is possible to reliably transfer the toner image onto the sheet P. 
     Further, since the contact point N is located on the upper side with respect to the guide protrusion  103  of the second sheet guide  89 , it is possible to secure a space for disposing the developing roller  26  and the rear part  144  of the developing bottom wall  140  on the front lower side of the photosensitive drum  20  and on the upper side of the second sheet guide  89 . 
     Further, the developing roller  26  is disposed on the front lower side with respect to the photosensitive drum  20 , and the rear part  144  of the developing bottom wall  140  is disposed between the developing roller  26  and the second sheet guide  89  in the upper-lower direction. 
     Therefore, in an image forming operation, even if toner falls down when the toner is supplied from the developing roller  26  to the photosensitive drum  20 , the fallen toner is accumulated on the upper surface of the rear part  144  of the developing bottom wall  140 . As a result, it is possible to prevent the inside of the printer  1  from being contaminated due to the toner. 
     (4) Further, the scanner unit  16  is disposed so as to overlap the sheet feed roller  8  when projected in the upper-lower direction as shown in  FIG. 1 . Therefore, it is possible to achieve size-reduction of the printer  1  in the front-rear direction as compared with a case where the scanner unit  16  and the sheet feed roller  8  are arranged in the front-rear direction. 
     As a result, it is possible to achieve size-reduction of the printer  1  in each of the upper-lower direction and the front-rear direction. 
     Further, the sheet feed roller  8  and the scanner unit  16  overlap each other in the upper-lower direction, and thus the front part of the sheet discharge tray  35  is heightened by a height of the sheet feed roller  8 . In other words, a height of the front part of the sheet discharge tray  35  is approximate to a height of the sheet discharge port  68  disposed at the rear part of the sheet discharge tray  35 . Thus, it is possible to prevent the sheet P discharged to the sheet discharge tray  35  from dropping forward from the sheet discharge tray  35 . 
     (5) Further, the printer  1  includes the first transport rollers  100  and the second transport rollers  101  as shown in  FIG. 1 . Further, each of the first transport rollers  100  and the second transport rollers  101  transports the sheet P transported from the sheet feed roller  8  toward the photosensitive drum  20 , at a position located further rearward than the sheet feed roller  8 , that is, around the process cartridge  15 . As a result, the sheet P transported from the sheet feed roller  8  can be reliably transported to the photosensitive drum  20 . 
     (6) In the printer  1 , as shown in  FIG. 1 , the scanner unit  16  is disposed further forward than the process cartridge  15 , and the scanner unit  16  and the process cartridge  15  are disposed so as to be arranged in the front-rear direction along the sheet guide section  6 . 
     Therefore, it is possible to achieve size-reduction of the printer  1  in the vertical direction. 
     (7) Further, toner accommodated in the developing frame  25  is supplied to the developing roller  26 , and is then supplied to the photosensitive drum  20  by the developing roller  26 , as shown in  FIG. 1 . Therefore, the process cartridge  15  can reliably form a toner image on the sheet P. 
     Furthermore, the developing frame  25  and the developing roller  26  are disposed so as to be arranged in the front-rear direction along the sheet guide section  6 . That is, the scanner unit  16 , the developing frame  25 , and the developing roller  26  are disposed so as to be arranged in the front-rear direction along the sheet guide section  6 . 
     Therefore, while the process cartridge  15  includes the developing frame  25  and the developing roller  26 , the printer  1  can reliably achieve size-reduction in the vertical direction. 
     (8) Further, the process cartridge  15  can be removably mounted to the main body casing  2  as shown in  FIGS. 1 to 3 . Therefore, it is possible to improve maintenance property of the process cartridge  15 . 
     (9) According to the printer  1 , as shown in  FIGS. 1 and 2 , when the top cover  77  of the main body casing  2  is moved from the closed position to the open position, the protrusion  134  of the process cartridge  15  is engaged with the engagement portion  82  of the cover guide  80 , and thus the process cartridge  15  is moved from the internal position to the extraction position. Further, the handle  115  of the process cartridge  15  is moved from the accommodation position to the ejection position in interlocking with the movement of the process cartridge  15  from the internal position to the extraction position. 
     Therefore, if the top cover  77  is moved from the closed position to the open position, the process cartridge  15  can be moved from the internal position to the extraction position, and the handle  115  of the process cartridge  15  can also be moved to the ejection position. In a state where the handle  115  is located at the ejection position, the handle body  125  is inclined so as to fall forward from the drum front wall  111  with the swing shaft  126  as a fulcrum. That is, in the state where the handle  115  is located at the ejection position, the grip portion  129  of the handle  115  is located outside the main body casing  2 , and is thus located on the upper side of the connection part between the inclined wall  70  and the guide wall  71 , that is, on the upstream side of the process cartridge  15  in the mounting direction. 
     As a result, the grip portion  129  of the handle  115  can be easily held, and thus the process cartridge  15  can be easily pulled out toward the upstream side in the mounting direction. 
     Therefore, the process cartridge  15  can be mounted to and removed from the main body casing  2  without opening the top cover  77  largely. 
     (10) Further, according to the printer  1 , as shown in  FIGS. 1 and 2 , the process cartridge  15  is guided by the second groove  56  of the groove  46  when the process cartridge  15  is interlocked with a movement of the top cover  77  between the closed position and the open position. 
     Therefore, the process cartridge  15  can be reliably moved between the internal position and the extraction position in interlocking with the movement of the top cover  77 . 
     (11) According to the printer  1 , as shown in  FIGS. 1 and 2 , the second groove  56  has a substantially arc shape with a center at the rotation shaft  78  when viewed from the left-right direction, and thus it is possible to smoothly guide the process cartridge  15  which is interlocked with a movement of the top cover  77 . 
     Therefore, the process cartridge  15  can be reliably positioned in the main body casing  2 . 
     (12) Further, according to the printer  1 , as shown in  FIGS. 1 and 2 , the cover guide  80  can be moved so as to follow a movement of the top cover  77  between the closed position and the open position. 
     Therefore, when the top cover  77  is located at the closed position, the cover guide  80  can be accommodated in the main body casing  2  along with the process cartridge  15  located at the internal position. 
     Further, when the process cartridge  15  is moved from the internal position to the extraction position, the protrusion  134  of the process cartridge  15  is engaged with the engagement portion  82  of the cover guide  80 , and thus the cover guide  80  is located outside the main body casing  2  in following a movement of the top cover  77 . 
     As a result, as shown in  FIG. 3 , the process cartridge  15  can be easily pulled out from the extraction position to the external position by using the cover guide  80  which is located outside the main body casing  2 . 
     (13) Further, according to the printer  1 , as shown in  FIGS. 2 and 3 , the cover guide  80  extends in the mounting direction X of the process cartridge  15 . 
     Therefore, when the process cartridge  15  located at the extraction position is moved to the external position outside the main body casing  2 , the process cartridge  15  can be guided in the mounting direction X. 
     As a result, the process cartridge  15  can be easily mounted to and removed from the main body casing  2 . 
     (14) Further, according to the printer  1 , as shown in  FIGS. 2 and 3 , since the process cartridge  15  is located at a position where the handle  115  is separated from the rotation shaft  78  of the top cover  77  and a position where the cover guide  80  is separated from the rotation shaft  78  of the top cover  77 , the process cartridge  15  can be mounted and removed in the mounting direction intersecting the rotation shaft  78 . 
     Therefore, the process cartridge  15  can be mounted to and removed from the main body casing  2  without opening the top cover  77  largely as compared with a case where the process cartridge  15  is mounted and removed along the rotation shaft  78 . 
     (15) Further, according to the printer  1 , as shown in  FIG. 4 , the cover guides  80  are respectively disposed at both left and right ends of the top cover  77 , and thus can guide the pair of protrusions  134  disposed on both left and right outsides of the process cartridge  15 , that is, the left and right outer surfaces of the process cartridge  15 . 
     Therefore, both left and right ends of the process cartridge  15  are supported at two locations, and thus a movement between the extraction position and the external position can be stably performed. 
     (16) Further, according to the printer  1 , as shown in  FIG. 1 , when an image is formed, the cover guide  80  is disposed further outward in the left-right direction than the scanner unit  16  so as not to interfere with exposure of the photosensitive drum  20  from the scanner unit  16 . 
     Therefore, it is possible to reliably form an electrostatic latent image on the photosensitive drum  20 . 
     Further, according to the printer  1 , as shown in  FIG. 1 , when the top cover  77  is located at the closed position, that is, the process cartridge  15  is located at the internal position, the scanner unit  16  and the cover guide  80  overlap each other when projected in the left-right direction. That is, the cover guide  80  is stored in the main body casing  2  so as to be disposed outside the scanner unit  16  in the left-right direction. 
     Therefore, it is possible to achieve size-reduction of the printer  1  in the vertical direction. 
     (17) Further, according to the printer  1 , as shown in  FIG. 3 , the mounting/removing guide wall  67  disposed on the upper side with respect to the scanner unit  16  guides a movement of the process cartridge  15  between the extraction position and the external position. 
     Therefore, not only the cover guide  80  but also the mounting/removing guide wall  67  can more reliably guide a movement of the process cartridge  15  between the extraction position and the external position by using a narrow space between the top cover  77  and the scanner unit  16 . 
     (18) Further, according to the printer  1 , as shown in  FIGS. 1 and 2 , the engagement portion  82  of the cover guide  80  can be moved so as to follow a movement of the top cover  77  between the closed position and the open position. 
     Therefore, the process cartridge  15  can be moved in interlocking with a movement of the top cover  77  while the protrusion  134  and the engagement portion  82  (an example of an interlocking mechanism) are engaged with each other. 
     (19) Further, according to the printer  1 , as shown in  FIGS. 1 and 2 , when the process cartridge  15  is moved from the internal position to the extraction position which is located on the upper side with respect to the internal position, the handle  115  is inclined so as to become separated forward from the drum front wall  111  due to the self-weight of the handle body  125  with the swing shaft  126  as a fulcrum, and is thus moved from the accommodation position to the ejection position. 
     Therefore, the handle  115  can be easily moved from the accommodation position to the ejection position. 
     (20) Further, according to the printer  1 , as shown in  FIG. 3 , since the process cartridge  15  can be mounted to and removed from the main body casing  2  without opening the top cover  77  largely, it is possible to prevent a size of the printer  1  from being increased in the vertical direction even if the flat bed scanner  40  is provided on the upper side of the main body casing  2 . 
     Incidentally, in the first illustrative embodiment, the printer  1  is an example of an image forming apparatus; the main body casing  2  is an example of a casing; the sheet guide section  6  is an example of a transport guide; the sheet feed cassette  7  is an example of a cassette; and the sheet feed roller  8  is an example of a first roller. Further, the process cartridge  15  is an example of a process unit; the scanner unit  16  is an example of an exposure unit; and the fixing unit  17  is an example of a fixing unit. Furthermore, the developing cartridge  19  is an example of a developing unit; the photosensitive drum  20  is an example of a photosensitive body; and the transfer roller  21  is an example of a transfer member. Moreover, the developing frame  25  is an example of a developer accommodation portion and a first developer accommodation portion; the developing roller  26  is an example of a developer carrier; the sheet discharge rollers  34  is an example of a second roller; the sheet discharge tray  35  is an example of a discharge portion and a tray; and the flat bed scanner  40  is an example of an image reading unit. Further, the bottom wall  53  is an example of one side wall; the second groove  56  is an example of a guide portion; and the small width portion  58  is an example of a first guide portion. Further, the sheet opening  61  is an example of a first opening; the mounting/removing guide wall  67  is an example of a wall portion; the process opening  75  is an example of an opening; the top cover  77  is an example of a cover; the rotation shaft  78  is an example of a rotation shaft; the cover guide  80  is an example of a second guide portion; the left cover guide  80 L is an example of one guide; and the right cover guide  80 R is an example of the other guide. Furthermore, the first sheet guide  88  is an example of a first guide, and the downstream part  96  is an example of a downstream part of the first guide in a transport direction. Moreover, the first transport rollers  100  are examples of a third roller and a fifth roller, and the second transport rollers  101  are examples of a third roller and a sixth roller. Further, the guide part  107  is an example of a second guide, and the guide protrusion  103  is an example of a downstream end of the second guide in the transport direction. The handle  115  is an example of a handle; the handle body  125  is an example of a body portion; and the swing shaft  126  is an example of a swing shaft. Further, the protrusion  134  is an example of a protrusion; the engagement portion  82  is an example of an engagement portion; and the protrusion  134  and the engagement portion  82  are an example of an interlocking mechanism. Further, the sheet P is an example of a recording medium, and the contact point N is an example of a contact part. 
     8. Second Illustrative Embodiment 
     Next, with reference to  FIGS. 8 to 12 , a second illustrative embodiment of the printer  1  will be described. In the second illustrative embodiment, the same members as in the first illustrative embodiment are given the same reference numerals, and description thereof will be omitted. Further, among operations in the second illustrative embodiment, the same operation in the first illustrative embodiment will not be repeated. 
     In the second illustrative embodiment, the scanner unit  16  is adjacent to the process cartridge  15  on the front side and is disposed on the rear upper side with respect to the sheet feed roller  8  with an interval therebetween as shown in  FIG. 8 . Specifically, the scanner unit  16  is disposed between the process cartridge  15  and the sheet feed roller  8  in the front-rear direction when projected in the upper-lower direction. That is, the sheet feed roller  8  is disposed further forward than the process cartridge  15 . 
     (1) Details of Main Body Casing of Second Illustrative Embodiment 
     The front wall  52  of the main body casing  2  has a substantially crank shape in a side view, and includes a lower portion  152 , a stepped portion  153 , and an upper portion  154  which are integrally formed. 
     The lower portion  152  is a lower part of the front wall  52 . The lower portion  152  is a substantially plate shape extending in the upper-lower direction in a side view, and includes a cassette opening  60 . The cassette opening  60  is disposed at a lower end of the lower portion  152 . 
     The stepped portion  153  has a plate shape extending in the front-rear direction in a side view, and is bent from an upper end of the lower portion  152  and extends rearward. 
     The upper portion  154  is an upper part of the front wall  52  and is located further rearward than the lower portion  152 . The upper portion  154  has a substantially plate shape extending in the upper-lower direction in a side view, and is bent from a rear end of the stepped portion  153  and extends upward. The upper portion  154  has a sheet opening  61 . The sheet opening  61  is disposed at a lower end of the upper portion  154 . 
     The top wall  54  of the main body casing  2  includes a sheet discharge wall  155 . 
     The sheet discharge wall  155  is disposed on the front side with respect to the tray wall  66  with an interval therebetween, and is disposed on the front upper side with respect to the scanner unit  16 . The sheet discharge wall  155  is disposed so as to overlap the front end of the scanner unit  16 , a transport roller  192  (described later), a sheet feed roller  193  (described later), and a pad  194  (described later), when projected in the upper-lower direction. 
     The sheet discharge wall  155  is connected to the upper end of the front wall  52 , and extends toward the rear upper side and in the left-right direction. Both left and right ends of the sheet discharge wall  155  are connected to upper ends of the front parts  64  of the respective side walls  50 . The sheet discharge wall  155  includes a sheet discharge wall body  157  and a bent portion  158  which are integrally formed. 
     The sheet discharge wall body  157  is connected to the upper end of the front wall  52 , and extends so as to be inclined upward rearward. The sheet discharge wall body  157  is provided with a regulation receiving groove  156  and a sheet regulation portion  159 . 
     The regulation receiving groove  156  is disposed at a substantially center part of the sheet discharge wall body  157  in the front-rear direction and the left-right direction. 
     The sheet regulation portion  159  is a substantially rectangular plate shape in a plan view. The sheet regulation portion  159  is moved between an inclined position where the sheet regulation portion  159  is accommodated in the regulation receiving groove  156  and is disposed along the sheet discharge wall body  157 , and a standing position where the sheet regulation portion  159  is rotated in the clockwise direction in a left side view with a front end thereof as a fulcrum and stands up so as to extend toward the front upper side from the sheet discharge wall body  157 . In a state where a movable tray  171  (described later) is located at a first position, the sheet regulation portion  159  is moved between the inclined position and the standing position via a base portion opening  184  and an extension portion opening  185 . 
     The bent portion  158  is disposed at a rear end of the sheet discharge wall  155 . The bent portion  158 , which has a substantially crank shape in a side view, protrudes downward from the rear end of the sheet discharge wall body  157 , is then bent rearward, and is subsequently bent downward. 
     That is, an engagement portion  160  is defined by the rear end of the sheet discharge wall body  157  and the bent part of the bent portion  158 . The engagement portion  160  is recessed in a substantially rectangular shape in a side view from the rear upper side toward the front lower side over the sheet discharge wall  155  in the left-right direction. 
     The main body casing  2  includes a scanner unit accommodation portion  163 . 
     The scanner unit accommodation portion  163  has a substantially box shape which is opened rearward, and accommodates the scanner unit  16  in an inner space thereof. The scanner unit accommodation portion  163  includes an accommodation portion front wall  164 , an accommodation portion top wall  165 , and an accommodation portion bottom wall  166 . 
     The accommodation portion front wall  164  is disposed at a front end of the scanner unit accommodation portion  163 . The accommodation portion front wall  164  has a substantially rectangular plate shape extending in the left-right direction in a front view. Both left and right ends of the accommodation portion front wall  164  are connected to inner surfaces in the left-right direction of the front parts  64  of the respective side walls  50 . 
     The accommodation portion top wall  165  is disposed at the upper end of the scanner unit accommodation portion  163 . The accommodation portion top wall  165  has a substantially plate shape extending in a direction which connects the front upper side and the rear lower side. The accommodation portion top wall  165  includes an inclined wall  167 , a guide wall  168 , and a regulation wall  169 . 
     The inclined wall  167  is connected to the upper end of the accommodation portion front wall  164 , extends so as to be inclined upward rearward, is then bent, and extends so as to be inclined downward rearward. 
     The guide wall  168  is bent from a rear end of the inclined wall  167  so that a downward inclination thereof is larger than that of the inclined wall  167 , and extends so as to be inclined downward rearward. 
     The regulation wall  169  is bent from a rear end of the guide wall  168  so that a downward inclination thereof is larger than that of the guide wall  168 , is inclined downward rearward, and is further bent so as to protrude downward. 
     The accommodation portion top wall  165  includes, as shown in  FIG. 11 , cutout portions  73  at respective ends thereof in the left-right direction. The cutout portions  73  correspond to the cover guides  80 , and are cut out in a substantially rectangular shape in a plan view from ends of the regulation wall  169  in the left-right direction up to an approximately center of the inclined wall  167  in the front-rear direction. 
     The accommodation portion bottom wall  166  is disposed at a lower end of the scanner unit accommodation portion  163  as shown in  FIG. 8 . The accommodation portion bottom wall  166  has a substantially rectangular plate shape extending in the left-right direction in a bottom view. A front end of the accommodation portion bottom wall  166  is connected to the lower end of the accommodation portion front wall  164 , and both left and right ends of the accommodation portion bottom wall  166  are connected to the inner surfaces in the left-right direction of the front parts  64  of the respective side walls  50 . 
     In a similar manner to in the first illustrative embodiment, the top cover  77  can swing between a closed position where the process opening  75  is closed as shown in  FIG. 8 , and an open position where the process opening  75  is opened as shown in  FIG. 9 , with the rotation shaft  78  as a fulcrum. 
     As shown in  FIG. 8 , in a state where the top cover  77  is located at the closed position, the cover body  79  is disposed so as to extend forward from the rotation shaft  78 , and a front end of the cover body  79  is fitted in the engagement portion  160 . Thus, the front surface of the tray wall  66 , the upper surface of the cover body  79 , and the upper surface of the sheet discharge wall  155  configure the sheet discharge tray  35 . The front part of the guide body  86  is disposed inside the first groove  47  of the groove  46  via the cutout portion  73 , and thus each of both of the left and right cover guides  80  is disposed with respect to the scanner unit  16  with an interval therebetween in the left-right direction. Therefore, the introduction portion  85  of the guide body  86  overlaps the scanner unit  16  when projected in the left-right direction. 
     The cover body  79  includes a reception portion  162 . The reception portion  162  is disposed at a front end of the upper surface of the cover body  79  of the top cover  77 . The reception portion  162  is recessed in a substantially rectangular shape in a side view from the upper surface of the cover body  79  toward the rear lower side, and is opened toward the front lower side. 
     (2) Details of Sheet Guide Section of Second Illustrative Embodiment 
     In the first sheet guide  88 , the upstream part  94  and the middle part  95  are disposed further forward than the scanner unit  16 . On the other hand, the downstream part  96  of the first sheet guide  88  is disposed on the lower side of the scanner unit  16  so as to overlap the scanner unit  16  when projected in the upper-lower direction. 
     The downstream part  96  includes the pair of first transport rollers  100 , the pair of second transport rollers  101 , and an inclined guide  99 . 
     The pair of first transport rollers  100  are disposed to be adjacent to the rear end of the linear guide  98  on the rear side, and is also disposed further forward than the scanner unit  16 . The pair of first transport rollers  100  is disposed further rearward than the sheet feed roller  8 . 
     The pair of second transport rollers  101  are disposed on the rear lower side with respect to the pair of first transport rollers  100  with an interval therebetween, and is disposed further rearward than the scanner unit  16 . 
     The inclined guide  99  is disposed between the pair of first transport rollers  100  and the pair of second transport rollers  101 . The inclined guide  99  is disposed on the lower side so as to be parallel to the accommodation portion bottom wall  166  of the scanner unit accommodation portion  163  with an interval therebetween. That is, the accommodation portion bottom wall  166  configures the downstream part  96  of the first sheet guide  88  along with the pair of first transport rollers  100 , the pair of second transport rollers  101 , and the inclined guide  99 . 
     The fifth sheet guide  92  of the sheet guide section  6  is disposed on the upper side of the middle part  95  of the first sheet guide  88  and the front side of the scanner unit  16 , at the front end of the main body casing  2 . The fifth sheet guide  92  guides transport of the sheet P which is supplied from outside of the main body casing  2  via the sheet opening  61  and is directed toward the pair of first transport rollers  100 . The fifth sheet guide  92  includes the transport roller  192 , the sheet feed roller  193 , the lower plate  109 , and the pad  194 . 
     The transport roller  192  has a substantially columnar shape extending in the left-right direction, and is disposed on the rear side with respect to the sheet opening  61 . 
     The sheet feed roller  193  has a substantially columnar shape extending in the left-right direction, and is disposed on the rear side with respect to the transport roller  192 . 
     The lower plate  109  extends rearward from a lower edge of the sheet opening  61  of the front wall  52  in a side view. The lower plate  109  is disposed on the lower side with respect to the transport roller  192  and the sheet feed roller  193  with an interval therebetween. 
     The lower plate  109  is connected to the rear end of the curved guide  97 . Thus, the fifth sheet guide  92  and the middle part  95  of the first sheet guide  88  are connected to each other on the front side of the pair of first transport rollers  100 . 
     The pad  194  is disposed on the lower side of the sheet feed roller  193 , and is supported at a rear end of the upper surface of the lower plate  109 . The pad  194  has a plate shape, and extends in a direction which connects the front upper side and the rear lower side in a side view. The upper surface of the pad  194  is in contact with a lower end of the sheet feed roller  193 . 
     (3) Details of Movable Tray 
     The main body casing  2  includes the movable tray  171  as shown in  FIGS. 9 and 12 . Although described later in detail, the movable tray  171  is moved between a first position where the movable tray  171  is bent along an exterior of the main body casing  2  as shown in  FIG. 8 , and a second position where the movable tray  171  extends forward from the main body casing  2  as shown in  FIG. 9 . 
     The following description of the movable tray  171  will be made with a state where the movable tray  171  is located at the second position as a reference. 
     As shown in  FIG. 9 , the movable tray  171  includes a first movable shaft  174 , a first part  175 , a second movable shaft  176 , and a second part  177 . 
     The first movable shaft  174 , which has a substantially columnar shape extending in the left-right direction, is disposed over the upper surface of the stepped portion  153  of the front wall  52 , that is, on the front side of a lower edge of the sheet opening  61 , and is rotatably supported at the front ends of the front parts  64  of both of the side walls  50 . 
     The first part  175  has a plate shape, and extends outward in a radial direction of the first movable shaft  174  from the first movable shaft  174 . The first part  175  includes a pair of regulation portion grooves  178  and a pair of supply regulation portions  179 , as shown in  FIG. 12 . 
     The pair of regulation portion grooves  178  are grooves which extend in the left-right direction on the upper surface of the first part  175 , and are disposed with an interval therebetween in the left-right direction. 
     The pair of supply regulation portions  179  are disposed on the upper surface of the first part  175  as shown in  FIG. 9 . Each of the pair of supply regulation portions  179  has a substantially rectangular plate shape extending in the front-rear direction in a side view. Each of the pair of supply regulation portions  179  is slidable in the left-right direction along the corresponding regulation portion groove  178 . The pair of supply regulation portions  179  are interlocked with each other by a link mechanism (not shown), and if one supply regulation portion  179  is slid and moved inward in the left-right direction, the other supply regulation portion  179  is also slid and moved inward in the left-right direction. Furthermore, if one supply regulation portion  179  is slid and moved outward in the left-right direction, the other supply regulation portion  179  is also slid and moved outward in the left-right direction. 
     The second movable shaft  176  has a substantially columnar shape extending in the left-right direction, and is rotatably supported at an end of the first part  175  on an opposite side to the first movable shaft  174 , that is, at a front end thereof. 
     The second part  177  includes a base portion  182  and an extension portion  183 . 
     The base portion  182  has a substantially rectangular plate shape in a plan view, and extends outward in a radial direction of the second movable shaft  176  from the second movable shaft  176 . The base portion  182  includes the base portion opening  184 . The base portion opening  184  is disposed from a substantially center of the base portion  182  in the front-rear direction to a rear part thereof at a substantially center of the base portion  182  in the left-right direction. The base portion opening  184  has a substantially rectangular shape extending in a plan view, and penetrates through the base portion  182  in the upper-lower direction. A dimension of the base portion opening  184  in the left-right direction is slightly larger than a dimension of the sheet regulation portion  159  in the left-right direction. 
     The extension portion  183  has a plate shape extending in the same direction as the base portion  182 . The extension portion  183  is slid and moved with respect to the base portion  182  between a retreat position where the extension portion  183  overlaps an upper surface of the base portion  182  as indicated by a dashed line in  FIG. 9 , and an advance position where the extension portion  183  extends further forward from the base portion  182  as indicated by a solid line in  FIG. 9 . The extension portion  183  includes the extension portion opening  185 . 
     The extension portion opening  185  is disposed so as to overlap the base portion opening  184  of the base portion  182  in a state where the extension portion  183  is located at the retreat position. Specifically, the extension portion opening  185  has a substantially U shape which is opened rearward in a plan view, and is cut out forward from a substantially center part in the front-rear direction at a rear edge of the extension portion  183 . A dimension of the extension portion opening  185  in the left-right direction is the same as a dimension of the base portion opening  184  in the left-right direction. 
     A dimension of the second part  177  viewed from the left-right direction is larger than a dimension of the first part  175  viewed from the left-right direction in both states where the extension portion  183  is located at the retreat position or the advance position. 
     Further, the movable tray  171  is rotated between a first position where the movable tray  171  is bent along the exterior of the main body casing  2  so that the second part  177  covers the sheet discharge wall  155  and the front end of the sheet discharge tray  35  as shown in  FIG. 8 , and a second position where the movable tray  171  extends in a direction which linearly connects the front upper side and the rear lower side in a side view so as to become separated from the main body casing  2  as shown in  FIG. 9 , with the first movable shaft  174  as a fulcrum. 
     A downstream surface of the movable tray  171  in the clockwise direction in a left side view is referred to as a front surface  188 , and an upstream surface thereof in the clockwise direction in a left side view is referred to as a rear surface  189 . 
     As shown in  FIG. 8 , in a state where the movable tray  171  is located at the first position, the first part  175  is disposed so as to extend upward from the first movable shaft  174 . The second part  177  is disposed so as to extend toward the rear upper side from the upper end of the first part  175 , that is, the second movable shaft  176  when the extension portion  183  thereof is located at the retreat position. Thus, the second part  177  covers the upper portion  154  of the front wall  52  and the sheet discharge wall body  157  of the sheet discharge wall  155 , and the rear upper end thereof is received by the reception portion  162  of the cover body  79 . That is, in a state where the movable tray  171  is located at the first position, the sheet discharge tray  35  is formed by the front surface of the tray wall  66 , the upper surface of the cover body  79 , and the front surface  188  of the movable tray  171  at the second part  177 . Accordingly, the front surface  188  receives a discharged sheet P when the movable tray  171  is located at the first position. 
     As shown in  FIG. 10 , in a state where the movable tray  171  is located at the second position, the first part  175  is disposed so as to extend toward the front upper side from the first movable shaft  174 . The second part  177  is disposed so as to extend toward the front upper side from the front upper end of the first part  175 , that is, the second movable shaft  176  so that an upward inclination thereof is larger than that of the first part  175 , when the extension portion  183  thereof is located at the advance position. That is, the movable tray  171  extends substantially linearly in a direction which connects the rear lower side to the front upper side in a side view in a state of being located at the second position. Thus, the movable tray  171  located at the second position allows a sheet P to be placed on the rear surface  189 , and thus guides the supply of the sheet P into the main body casing  2  via the sheet opening  61 . As mentioned above, the rear surface  189  receives a sheet P which is transported into the main body casing  2  from outside via the sheet opening  61  when the movable tray  171  is located at the second position. In a state where the movable tray  171  is located at the second position, the sheet discharge tray  35  is formed by the front surface of the tray wall  66 , the upper surface of the cover body  79 , and the upper surface of the sheet discharge wall body  157  of the sheet discharge wall  155 . 
     (4) Removing and Mounting Operations of Process Cartridge with Respect to Main Body Casing 
     Next, a removing operation and a mounting operation of the process cartridge  15  with respect to the main body casing  2  will be described. 
     (4-1) Removing Operation of Process Cartridge from Main Body Casing 
     First, a description will be made of a removing operation of the process cartridge  15  from the main body casing  2 , that is, a movement of the process cartridge  15  from the internal position to the external position. 
     As shown in  FIG. 8 , in a state where the process cartridge  15  is located at the internal position, the front surface of the grip portion  129  of the handle  115  is in contact with the regulation wall  169  of the scanner unit accommodation portion  163 . Therefore, the handle  115  is located at the accommodation position inside the main body casing  2 . 
     In order to move the process cartridge  15  from the internal position to the external position, as shown in  FIG. 9 , the operator swings the flat bed scanner  40  in the counterclockwise direction in a left side view, and also moves the movable tray  171  from the first position to the second position. At this time, the extension portion  183  of the second part  177  is located at the retreat position, and thus a rotation radius is reduced when the movable tray  171  is rotated with the first movable shaft  174  as a fulcrum. Therefore, it is possible to reduce a displacement amount of the swing of the flat bed scanner  40  in the counterclockwise direction in a left side view. The flat bed scanner  40  is swung so that the movable tray  171  is located at the second position, and then the top cover  77  is moved from the closed position to the open position. 
     Accordingly, contact between the grip portion  129  and the regulation wall  169  is released, and the handle  115  is moved from the accommodation position to the ejection position by the gravity. 
     Thus, the process cartridge  15  is taken out from the internal position to the extraction position in interlocking with the movement of the top cover  77  from the closed position to the open position, and the handle  115  is moved from the accommodation position to the ejection position in interlocking with the movement of the process cartridge  15  from the internal position to the extraction position. 
     Next, the operator, as shown in  FIGS. 9 and 10 , holds the grip portion  129  of the handle  115  located at the ejection position, and pulls out the process cartridge  15  toward the front upper side in the removing direction Y. 
     In the course of the pulling-out, the contact portion  117  and the transfer accommodation wall  113  of the drum frame  23  reach the upper side of the guide wall  168 , and are slid on the guide wall  168 . The guide wall  168  guides the contact portion  117  and the roller accommodation portion  122 , and thus the process cartridge  15  is moved forward and is removed from the main body casing  2 . 
     Accordingly, the process cartridge  15  passes through the process opening  75  from the internal position, and reaches the external position via the extraction position. 
     That is, the cover guide  80  and the accommodation portion top wall  165  guide a movement of the process cartridge  15  from the extraction position to the external position. 
     Next, the operator moves the top cover  77  from the open position to the closed position so as to move the movable tray  171  from the second position to the first position, and then swings the flat bed scanner  40  in the clockwise direction in a left side view until the flat bed scanner  40  is brought into contact with the flat bed support wall  65 . 
     In the above-described manner, the removing operation of the process cartridge  15  from the main body casing  2  is completed. 
     (4-2) Mounting Operation of Process Cartridge to Main Body Casing 
     In order to mount the process cartridge  15  to the main body casing  2 , procedures are performed in a reverse order to the above-described removing operation. 
     Specifically, as shown in  FIGS. 9 and 10 , the operator swings the flat bed scanner  40  in the counterclockwise direction in a left side view. Next, the movable tray  171  is moved from the first position to the second position, and then the top cover  77  is moved from the closed position to the open position. 
     Next, the operator moves the process cartridge  15  from the external position to the extraction position. 
     Successively, the operator moves the top cover  77  from the open position to the closed position, and also swings the flat bed scanner  40  in the clockwise direction in a left side view. 
     When the process cartridge  15  reaches the internal position from the extraction position, the handle  115  is located at the accommodation position while the grip portion  129  is disposed to be adjacent to the regulation wall  169  of the scanner unit accommodation portion  163  on the rear upper side. 
     In the above-described manner, the mounting operation of the process cartridge  15  to the main body casing  2  is completed. 
     (5) Sheet Feed Operation from Outside of Main Body Casing 
     If sheet sheets P are to be supplied from outside of the main body casing  2 , the operator places the sheet sheets P on the rear surface  189  of the movable tray  171  located at the second position. Therefore, the sheet sheets P are moved toward the rear lower side along the inclination of the second part  177 . Thus, rear ends of the sheet sheets P are located inside the main body casing  2  via the sheet opening  61 , and come into contact with the front lower end of the transport roller  192 . The pair of supply regulation portion  179  comes into contact with both left and right ends of rear parts of the sheets P, and regulates a movement of the sheets P in the left-right direction. 
     The transport roller  192  is rotated, and thus the sheets P are sent toward the sheet feed roller  193 . Therefore, the sheets Preach between the sheet feed roller  193  and the pad  194 . 
     Next, the sheet feed roller  193  is rotated, and thus the sheets P which reach between the sheet feed roller  193  and the pad  194  are separated one by one, so as to be sent toward the pair of first transport rollers  100 . Then, one sheet P separated by the sheet feed roller  193  reaches between the pair of first transport rollers  100 . 
     Thus, the sheet P supplied from the outside of the main body casing  2  is transported along the transport path T with a substantially S shape in a side view, which is defined by the sheet guide section  6 , allows an image to be formed thereon by the image forming section  4 , and is discharged to the sheet discharge tray  35 . 
     If the sheet regulation portion  159  is disposed at the standing position, the sheet regulation portion  159  prevents the sheet P discharged to the sheet discharge tray  35  from falling down from the sheet discharge tray  35 . 
     (6) Operations and Effects of Second Illustrative Embodiment 
     (6-1) The scanner unit  16  is disposed further rearward than the sheet feed roller  8  as shown in  FIG. 8 . Therefore, it is possible to reliably achieve size-reduction of the printer  1  in the vertical direction as compared with a case where the scanner unit  16  and the sheet feed roller  8  are arranged in the vertical direction. 
     (6-2) The sheet feed roller  193  transports a sheet P which is supplied from outside of the main body casing  2 , toward the photosensitive drum  20 . Therefore, it is possible to form a toner image on the sheet P supplied from outside of the main body casing  2 . 
     The sheet feed roller  193  is disposed further forward than the scanner unit  16 . Therefore, it is possible to prevent a size of the printer  1  from being increased in the vertical direction. 
     That is, it is possible to form a toner image on a sheet P supplied from outside of the main body casing  2 , and also to prevent a size of the printer  1  from being increased in the vertical direction. 
     (6-3) The scanner unit  16  is disposed between the first transport rollers  100  and the second transport rollers  101  when projected in the upper-lower direction as shown in  FIG. 8 . Therefore, it is possible to ensure an efficient arrangement of the scanner unit  16 , the first transport rollers  100 , and the second transport rollers  101 . 
     (6-4) According to the printer  1 , as shown in  FIG. 10 , in a case where the movable tray  171  is used, when the movable tray  171  is located at the second position, the movable tray  171  receives a sheet P, and the sheet P can be supplied into the main body casing  2  via the sheet opening  61  of the front wall  52 . 
     Further, as shown in  FIG. 8 , the movable tray  171  covers the front wall  52  of the main body casing  2  and the sheet discharge wall body  157  of the sheet discharge wall  155 , and the rear upper end thereof is received by the reception portion  162  of the cover body  79 , at the first position. That is, when the movable tray  171  is not used, the movable tray  171  can be accommodated while being located at the first position. 
     Therefore, the movable tray  171  does not extend in the vertical direction, and thus it is possible to achieve size-reduction of the printer  1  in the vertical direction. 
     (6-5) According to the printer  1 , as shown in  FIG. 10 , a sheet P is placed on the movable tray  171  located at the second position, and thus the sheet P can be reliably supplied into the main body casing  2  via the sheet opening  61  of the front wall  52 . 
     (6-6) According to the printer  1 , as shown in  FIG. 8 , the movable tray  171  is divided into two members including the first part  175  and the second part  177 , and thus the movable tray  171  can be easily folded back. 
     Therefore, when the movable tray  171  is located at the first position, the second part  177  is folded back toward the sheet discharge section  5 , and thus it is possible to achieve size-reduction of the printer  1  in the vertical direction. 
     (6-7) According to the printer  1 , as shown in  FIG. 8 , when the movable tray  171  is located at the first position, the reception portion  162  of the top cover  77  receives the rear upper end of the second part  177 , and thus the second part  177  can be configured as part of the sheet discharge section  5 . 
     Therefore, even if the movable tray  171  is located at the first position, and the second part  177  is folded back toward the sheet discharge section  5 , a sheet P can be discharged from the main body casing  2  without the second part  177  hindering the sheet P from being placed on the sheet discharge section  5 . 
     (6-8) According to the printer  1 , as shown in  FIG. 10 , the first part  175  and the second part  177  of the movable tray  171  located at the second position extend substantially linearly when viewed from the left-right direction. 
     Therefore, a sheet P can be stably placed on the movable tray  171  located at the second position. 
     As a result, the sheet P can be reliably supplied into the main body casing  2  via the sheet opening  61 . 
     (6-9) According to the printer  1 , as shown in  FIG. 12 , when a sheet P is placed on the movable tray  171  located at the second position, the supply regulation portion  179  can prevent an image formed on the sheet P from being displaced in the left-right direction due to a movement of the sheet P in the left-right direction. 
     Therefore, the sheet P can be more reliably supplied into the main body casing  2  via the sheet opening  61 . 
     (6-10) According to the printer  1 , as shown in  FIG. 8 , it is possible to prevent a discharged sheet P from falling down by using the sheet regulation portion  159  which is disposed so as to pass through the base portion opening  184  and the extension portion opening  185  even if the movable tray  171  is located at the first position. 
     Therefore, it is possible to regulate falling of the sheet P discharged to the sheet discharge section  5  by using the sheet regulation portion  159  even if the movable tray  171  is located either the first position or the second position. 
     (6-11) According to the printer  1 , as shown in  FIG. 8 , when the movable tray  171  is located at the first position, the second part  177  longer than the first part  175  can be folded back toward the sheet discharge section  5  when viewed from the left-right direction. 
     Therefore, when viewed from the left-right direction, the relatively long second part  177  of the movable tray  171  is disposed along the sheet discharge wall body  157  of the sheet discharge wall  155 , that is, folded back in a direction which connects the front lower side and the rear upper side, and thus the printer  1  can be size-reduced in the vertical direction even if the movable tray  171  is located at the first position. 
     (6-12) According to the printer  1 , as shown in  FIG. 8 , when the movable tray  171  is located at the first position, a discharged sheet P can be received by using the front surface  188 , and, as shown in  FIG. 10 , when the movable tray  171  is located at the second position, a sheet P which is supplied into the main body casing  2  from outside via the sheet opening  61  can be received by using the rear surface  189 . 
     Therefore, both surfaces of the movable tray  171  can be used. 
     (6-13) According to the printer  1 , as shown in  FIG. 9 , even if the flat bed scanner  40  is provided on the upper side with respect to the main body casing  2 , in the movable tray  171 , the second part  177  is rotated with the second movable shaft  176  as a fulcrum in a state where the extension portion  183  is located at the retreat position, and thus it is possible to reduce a rotation radius. 
     Therefore, the movable tray  171  can be moved between the first position and the second position without interfering with the flat bed scanner  40  simply by slightly swinging the flat bed scanner  40 . 
     Therefore, it is possible to prevent a size of the printer  1  in the vertical direction even if the flat bed scanner  40  is provided. 
     Also, in the second illustrative embodiment, it is possible to achieve the same operations and effects as in the above-described first illustrative embodiment. 
     Incidentally, in the second illustrative embodiment, the sheet regulation portion  159  is an example of a second regulation portion; the reception portion  162  is an example of a reception portion; and the accommodation portion top wall  165  is an example of a wall portion. The movable tray  171  is an example of a tray; the first part  175  is an example of a first part; and the second part  177  is an example of a second part. The supply regulation portion  179  is an example of a first regulation portion; the base portion opening  184  and the extension portion opening  185  are an example of a second opening; and the front surface  188  is an example of a first surface. The rear surface  189  is an example of a second surface, and the sheet feed roller  193  is an example of a fourth roller. 
     9. Third Illustrative Embodiment 
     Next, with reference to  FIGS. 13 to 19 , a third illustrative embodiment of the printer  1  will be described. In the third illustrative embodiment, the same members as in the first illustrative embodiment are given the same reference numerals, and description thereof will be omitted. Further, among operations in the third illustrative embodiment, the same operation in the first illustrative embodiment will not be repeated. 
     In the third illustrative embodiment of the present invention, the image forming section  4  includes a process unit  200 . 
     Although described later in detail, the process unit  200  can be moved between an internal position where the process unit  200  lies in the main body casing  2  and an external position where the process unit is removed from the main body casing  2 . In a state of being located at the internal position, the process unit  200  is disposed at a substantially center inside the main body casing  2  in a side view, and is disposed on the upper side with respect to a substantially center part of the sheet feed cassette  7  in the front-rear direction. That is, the sheet feed cassette  7  is disposed on the lower side with respect to the process unit  200 . 
     The process unit  200  includes a process cartridge  201  and a toner cartridge  202 . 
     The process cartridge  201  is a lower part of the process unit  200 , and includes a process frame  203 , a drum unit  204 , a developing unit  205 , and a transport unit  230 . 
     (1) Process Frame 
     As shown in  FIGS. 13 and 18A , the process frame  203  includes a pair of process side walls  206 , a process front wall  207 , a charger holding wall  112 , a transfer accommodation wall  113 , and a cartridge support wall  208  which are integrally formed. 
     As shown in  FIG. 18A , the pair of process side walls  206  are respectively disposed at both left and right ends of the process frame  203 , and are disposed with an interval therebetween in the left-right direction. Each of the pair of process side walls  206  has a substantially rectangular plate shape in a side view as shown in  FIG. 18B . 
     Of the pair of process side walls  206 , the left process side wall  206  includes a first reception groove  214 , a second reception groove  215 , a toner supply port  216 , and a toner return hole  217 . 
     The first reception groove  214  is disposed on a rear upper end of the process side wall  206 . The first reception groove  214  has a semicircular shape which is opened upward in a side view, and is recessed downward from a rear end of an upper edge of the process side wall  206 . 
     The first reception groove  214  is disposed along an outer circumferential surface of a first shutter  255  (described later). 
     The second reception groove  215  is disposed on a front with respect to the first reception groove  214  with an interval therebetween. The second reception groove  215  has a semicircular shape which is opened upward in a side view, and is recessed downward from the upper edge of the process side wall  206 . The second reception groove  215  is disposed along an outer circumferential surface of a reception cylinder  263  (described later). 
     The toner supply port  216  is disposed at a lower end of the process side wall  206 , and is disposed on the front lower side with respect to the first reception groove  214  with an interval therebetween. The toner supply port  216  has a substantially circular shape in a side view, and penetrates through the process side wall  206  in the left-right direction. 
     The toner return hole  217  is disposed on the front upper side with respect to the toner supply port  216 , and is disposed on the rear lower side with respect to the second reception groove  215  with an interval therebetween. The toner return hole  217  has a substantially circular shape in a side view, and penetrates through the process side wall  206  in the left-right direction. 
     As shown in  FIG. 16 , the process front wall  207  has a plate shape which extends in a direction which connects the front upper side to the rear lower side in a side view, and extends in the left-right direction. Each of both left and right ends of the process front wall  207  is connected to the front end of each process side wall  206 . The process front wall  207  includes a laser passing hole  124 . 
     The laser passing hole  124  is disposed at an upper end of the process front wall  207  so as to correspond to a light path of laser beam L. The laser passing hole  124  has a shape and a size which allow the laser beam L to pass through the laser passing hole  124 , and penetrates through the process front wall  207  in the front-rear direction. 
     The charger holding wall  112  is disposed at a rear upper end of the process frame  203 . Each of both left and right ends of the charger holding wall  112  is connected to the rear upper end of each process side wall  206 . 
     The transfer accommodation wall  113  is disposed at the rear lower end of the process frame  203 , and is disposed on the lower side with respect to the charger holding wall  112  with an interval therebetween. Each of both left and right ends of the transfer accommodation wall  113  is connected to the rear lower end of each process side wall  206 . 
     The cartridge support wall  208  has a plate shape which extends forward from the charger holding wall  112 , and extends in the left-right direction. Each of both left and right ends of the cartridge support wall  208  is connected to the upper end of each process side wall  206 . 
     The cartridge support wall  208  includes a connection portion  209 , an auger cylinder reception portion  210 , and a toner accommodation receiving portion  211  which are integrally formed. 
     The connection portion  209  is disposed to be adjacent to the transfer accommodation wall  113  on the front side, and has a plate shape which protrudes toward the front upper side from the front wall of the transfer accommodation wall  113 . 
     The auger cylinder reception portion  210  is disposed to be adjacent to the connection portion  209  on the front side. The auger cylinder reception portion  210  has a substantially C shape which is opened toward the front upper side in a side view, and is disposed along an outer circumferential surface of an auger accommodation cylinder  257  (described later). A rear end of the auger cylinder reception portion  210  is connected to the front end of the connection portion  209 . 
     The toner accommodation receiving portion  211  is disposed to be adjacent to the auger cylinder reception portion  210  on the front lower side. The toner accommodation receiving portion  211  has a substantially U plate shape in a side view, and is disposed along a lower end of a toner accommodation portion  258  (described later). 
     Specifically, the toner accommodation receiving portion  211  includes a rear reception portion  212  and a front reception portion  213 . The rear reception portion  212  is connected to the front end of the auger cylinder reception portion  210 , extends downward, and is then bent so as to extend forward. A front end of the rear reception portion  212  is connected to the upper end of the process front wall  207 . The front reception portion  213  extends toward the front upper side from the front end of the rear reception portion  212 . 
     (2) Drum Unit 
     The drum unit  204  is disposed at a rear end in the process frame  203 , and includes a photosensitive drum  20 , a transfer roller  21 , and a scorotron charger  22 . 
     The photosensitive drum  20  is disposed between the rear ends of the pair of process side walls  206 , and is disposed on the front lower side of the charger holding wall  112  and an upper side of the transfer accommodation wall  113 . The photosensitive drum  20  is rotatably supported at the process frame  203  while both left and right ends of the drum shaft  131  are supported at the respective process side walls  206 . The transfer roller  21  is rotatably supported at the process frame  203  while both left and right ends thereof are supported at the respective process side walls  206 . The scorotron charger  22  is supported at the charger holding wall  112 , and is thus supported at the process frame  203 . 
     (3) Developing Unit 
     The developing unit  205  is disposed on the front side of the drum unit  204  in the process frame  203 . The developing unit  205  includes a developing frame  220 , a first auger  218 , a second auger  219 , a developing roller  26 , a supply roller  27 , and a layer thickness regulation blade  28 . 
     The developing frame  220  has a hollow tubular shape extending in the left-right direction, and includes a first auger accommodation portion  222 , a second auger accommodation portion  223 , a blade support portion  138 , and a developing bottom wall  140  which are integrally formed. 
     The first auger accommodation portion  222  is disposed on a front lower end of the developing frame  220 . The first auger accommodation portion  222  has a substantially cylindrical shape extending in the left-right direction. Each of both left and right ends of the first auger accommodation portion  222  is continuous to an inner surface of each process side wall  206  in the left-right direction. Specifically, a left end of the first auger accommodation portion  222  is continuous to a circumferential edge of the toner supply port  216  of the left process side wall  206 . 
     The first auger accommodation portion  222  includes a toner opening  227 . The toner opening  227  is disposed at a rear end of the first auger accommodation portion  222 , and penetrates through the rear end of the first auger accommodation portion  222  in the front-rear direction. 
     The second auger accommodation portion  223  is disposed to be adjacent to the first auger accommodation portion  222  on the front upper side. The second auger accommodation portion  223  has a substantially cylindrical shape extending in the left-right direction. Each of both left and right ends of the second auger accommodation portion  223  is continuous to the inner surface of each process side wall  206  in the left-right direction. Specifically, a left end of the second auger accommodation portion  223  is continuous to a circumferential edge of the toner return hole  217  of the left process side wall  206 . 
     The rear lower end of the second auger accommodation portion  223  is continuous to the front upper end of the first auger accommodation portion  222  in the left-right direction. 
     The continuous part of the first auger accommodation portion  222  and the second auger accommodation portion  223  includes a communication hole  228 . As shown in  FIGS. 16 and 19 , the communication hole  228  is disposed at a right end of the continuous part of the first auger accommodation portion  222  and the second auger accommodation portion  223 , and penetrates through the continuous part in a direction which connects the front upper side and the rear lower side. Thus, an inner space of the first auger accommodation portion  222  communicates with an inner space of the second auger accommodation portion  223  via the communication hole  228 . 
     The blade support portion  138  is disposed to be adjacent to the second auger accommodation portion  223  on the rear side. The blade support portion  138  has a substantially rectangular shape which protrudes forward from the rear upper end of the second auger accommodation portion  223  in a side view. 
     The developing bottom wall  140  extends rearward from a lower circumferential edge of the toner opening  227  of the first auger accommodation portion  222 . Both left and right ends of the developing bottom wall  140  are connected to the inner surfaces of the respective process side walls  206  in the left-right direction. 
     The first auger  218  is disposed inside the first auger accommodation portion  222 . As shown in  FIG. 19 , the first auger  218  includes a first auger shaft  224  and a first auger screw  225 . 
     The first auger shaft  224  has a columnar shape extending in the left-right direction. A dimension of the first auger shaft  224  in the left-right direction is larger than a dimension of the developing frame  220  in the left-right direction. Therefore, a left end of the first auger shaft  224  protrudes further toward the left side than the left process side wall  206  via the toner supply port  216  as shown in  FIGS. 18B and 19 . 
     The first auger screw  225  is entirely disposed on a circumferential surface of the first auger shaft  224  in the left-right direction, and extends in a helical shape. The first auger  218  is rotatably supported at the process frame  203  while a right end of the first auger shaft  224  is supported at the right process side wall  206  and the left end of the first auger shaft  224  is supported at a supply closing plate  238  (described later). 
     The second auger  219  is disposed inside the second auger accommodation portion  223  as shown in  FIG. 16 . The second auger  219  includes a second auger shaft  272  and a second auger screw  273  as shown in  FIG. 19 . 
     The second auger shaft  272  has a columnar shape extending in the left-right direction. A dimension of the second auger shaft  272  in the left-right direction is larger than a dimension of the developing frame  220  in the left-right direction. Therefore, a left end of the second auger shaft  272  protrudes further toward the left side than the left process side wall  206  via the toner return hole  217  as shown in  FIGS. 18B and 19 . 
     The second auger screw  273  is disposed at a part located inside the developing frame  220  on a circumferential surface of the second auger shaft  272 , and extends in a helical shape. That is, the second auger screw  273  is not disposed on the circumferential surface at the left end of the second auger shaft  272 , which is located outside the developing frame  220 . 
     The second auger  219  is rotatably supported at the process frame  203  while a right end of the second auger shaft  272  is supported at the right process side wall  206  and the left end of the second auger shaft  272  is supported at a return closing plate  246  (described later). 
     As shown in  FIG. 16 , the developing roller  26  is disposed on the front upper side of the rear part  144  of the developing bottom wall  140  with an interval therebetween. The developing roller  26  is rotatably supported at the process frame  203  while both left and right ends of the developing roller shaft  146  are supported at the respective process side walls  206 . 
     The supply roller  27  is disposed inside the front part  143  of the developing bottom wall  140 . The supply roller  27  is rotatably supported at the process frame  203  while both left and right ends thereof are supported at the respective process side walls  206 . 
     The layer thickness regulation blade  28  is fixed to a read end of the blade support portion  138 . 
     (4) Transport Unit 
     The transport unit  230  is disposed on the left surface of the left process side wall  206  as shown in  FIG. 18B . The transport unit  230  includes a toner supply transport portion  233  and a toner return transport portion  234 . 
     The toner supply transport portion  233  transports toner from the auger accommodation cylinder  257  (described later) to the toner supply port  216 . 
     The toner supply transport portion  233  includes a supply transport frame  236 . The supply transport frame  236  extends in a direction which connects the front lower side to the rear upper side, and includes a first reception portion  235 , a supply circumferential side wall  239 , and the supply closing plate  238  which are integrally formed. 
     The first reception portion  235  has a substantially semicircular shape which is opened toward the rear upper side in a side view, and protrudes toward the left side from a circumferential edge of the first reception groove  214  of the left process side wall  206 . 
     The first reception portion  235  includes a toner supply reception hole  237 . The toner supply reception hole  237  is disposed at a front lower end of the first reception portion  235 , and penetrates through the first reception portion  235  in a direction which connects the front lower side to the rear upper side. 
     The supply circumferential side wall  239  has a substantially U shape which is opened toward the rear upper side in a side view, and protrudes the left surface of the left process side wall  206  toward the left side. Respective open ends, that is, upper ends of the supply circumferential side wall  239  are connected to the first reception portion  235 , and closed ends, that is, lower ends of the supply circumferential side wall  239  surround the toner supply port  216  in a left side view. 
     A lower end of the supply closing plate  238  rotatably supports the left end of the first auger shaft  224 . The supply closing plate  238  closes, as shown in  FIG. 19 , the left ends of the first reception portion  235  and the supply circumferential side wall  239 , and is disposed with respect to the left process side wall  206  with an interval therebetween. Thus, as shown in  FIG. 18B , a supply toner transport chamber  276  which is a closed space is defined by the process side wall  206 , the first reception portion  235 , the supply circumferential side wall  239 , and the supply closing plate  238 . The supply toner transport chamber  276  communicates with the inside of the developing frame  220  via the toner supply port  216 . 
     The toner return transport portion  234  transports toner discharged from the toner return hole  217  to the reception cylinder  263  (described later). 
     The toner return transport portion  234  is disposed on the front side of the toner supply transport portion  233 , and includes a return transport frame  241 , a reception portion shutter  244 , a belt shaft  242 , and a transport belt  243 . 
     The return transport frame  241  includes a second reception portion  240 , a return circumferential side wall  247 , a return closing plate  246 , and a closing wall  248  which are integrally formed. 
     The second reception portion  240  has a substantially semicircular shape which shares a center axis line with the second reception groove  215  in a side view, and is opened toward the front upper side. The second reception portion  240  extends in the left-right direction as shown in  FIG. 19 , and a right end of a lower part of the second reception portion  240  is connected to a circumferential edge of the second reception groove  215  of the left process side wall  206  as shown in  FIG. 18B . That is, an upper part of the second reception portion  240  is located on the upper side with respect to the upper edge of the process side wall  206 . 
     The return circumferential side wall  247  has a substantially elliptical shape extending in a direction which connects the front upper side to the rear lower side in a side view, and extends in the left-right direction. 
     A rear lower end of the return circumferential side wall  247  surrounds the toner return hole  217  in a left side view, and a front upper end of the return circumferential side wall  247  is connected to the upper part of the second reception portion  240 . That is, the front upper end of the return circumferential side wall  247  is located on the upper side with respect to the upper edge of the process side wall  206 . Further, in the right end of the return circumferential side wall  247 , a part located on the lower side with respect to the upper edge of the process side wall  206  is connected to the left surface of the process side wall  206 . 
     A connection part between the return circumferential side wall  247  and the second reception portion  240  includes a toner discharge hole  245 . The toner discharge hole  245  penetrates through the connection part between the return circumferential side wall  247  and the second reception portion  240  in a direction which connects the front lower side to the rear upper side. 
     The return closing plate  246  closes the left end of the return circumferential side wall  247  as shown in  FIG. 19 , and is disposed toward the left side with respect to the left process side wall  206  with an interval therebetween. A lower end of the return closing plate  246  rotatably supports the left end of the second auger shaft  272 . 
     The closing wall  248  closes a part located on the upper side with respect to the upper edge of the process side wall  206  in the right end of the return circumferential side wall  247 . A lower end of the closing wall  248  is connected to the upper edge of the process side wall  206 . 
     Thus, a tonner return transport chamber  277  which is a closed space is defined by the process side wall  206 , the return circumferential side wall  247 , the return closing plate  246 , and the closing wall  248 . The tonner return transport chamber  277  communicates with the inside of the developing frame  220  via the toner return hole  217 . 
     The reception portion shutter  244  is disposed on the second reception portion  240 . The reception portion shutter  244  is a thin plate with an arc shape in a side view, and is disposed along an inner circumferential surface of the second reception portion  240 . As indicated by a broken line, the reception portion shutter  244  is located on the front side of the toner discharge hole  245 , and is moved along the second reception portion  240  between a closed position where the toner discharge hole  245  is closed and an open position where the toner discharge hole  245  is opened. The reception portion shutter  244  is disposed at the closed position at the normal time. 
     The belt shaft  242  is disposed at an upper end in the tonner return transport chamber  277 . The belt shaft  242  has a substantially columnar shape extending in the left-right direction. A right end of the belt shaft  242  is rotatably supported at the closing wall  248 , and a left end of the belt shaft  242  is rotatably supported at the upper end of the return closing plate  246 . 
     The transport belt  243  is accommodated inside the tonner return transport chamber  277 . The transport belt  243  is wound around the left end of the second auger shaft  272  and the belt shaft  242 . An outer circumferential surface of the transport belt  243  includes a plurality of projections. Although described later in detail, the transport belt  243  is circumferentially moved so as to transport toner toward the front upper side through driving of the second auger shaft  272  and following movement of the belt shaft  242 . 
     (5) Toner Cartridge 
     The toner cartridge  202  is an upper part of the process unit  200  as shown in  FIGS. 14 and 16 , and is removably mounted to the process cartridge  201  (described later). 
     The toner cartridge  202  includes, as shown in  FIGS. 16 and 17A , a cartridge frame  251 , a first shutter  255 , a second shutter  256 , an auger member  252 , an agitator  253 , and an agitation member  254 . 
     The cartridge frame  251  has a substantially box shape extending in the left-right direction, and includes the auger accommodation cylinder  257  and the toner accommodation portion  258  which are integrally formed. The auger accommodation cylinder  257  and the toner accommodation portion  258  are disposed side by side on front and rear sides, and communicate with each other via a toner passing hole  261 . 
     The auger accommodation cylinder  257  is disposed at the rear end of the cartridge frame  251 . The auger accommodation cylinder  257  has a substantially cylindrical shape extending in the left-right direction, and each of both left and right ends is closed. A dimension of the auger accommodation cylinder  257  in the left-right direction is larger than a dimension of the toner accommodation portion  258  in the left-right direction as shown in  FIG. 17A . Further, a left end of the auger accommodation cylinder  257  is located on the further left side than a left end surface of the toner accommodation portion  258 . 
     The left end of the auger accommodation cylinder  257  includes a toner ejection hole  260 . As shown in  FIG. 18B , the toner ejection hole  260  is disposed at a front lower end of the left end of the auger accommodation cylinder  257 , and penetrates through the auger accommodation cylinder  257  in a direction which connects the front lower side to the rear upper side. 
     The toner accommodation portion  258  has an elliptically cylindrical shape extending in the left-right direction, and each of both left and right ends is closed. The toner accommodation portion  258  accommodates toner therein. The toner accommodation portion  258  includes an accommodation portion body  281  and a pair of accommodation portion side walls  280 . 
     The accommodation portion body  281  has an elliptically cylindrical shape extending in the left-right direction. A lower part of the accommodation portion body  281  has a shape extending along the toner accommodation receiving portion  211  as shown in  FIG. 16 , and a front part of a bottom wall of the accommodation portion body  281  is curved toward the front upper side. 
     The pair of accommodation portion side walls  280  are respectively disposed at both left and right ends of the toner accommodation portion  258 , and close both left and right ends of the accommodation portion body  281 . 
     Of the pair of accommodation portion side walls  280 , the left accommodation portion side wall  280  includes a toner return hole  262  and a reception cylinder  263  as shown in  FIG. 17A . The toner return hole  262  is disposed at a substantially center of the left accommodation portion side wall  280  in the front-rear direction. The toner return hole  262  has a substantially circular shape in a side view, and penetrates through the accommodation portion side wall  280  in the left-right direction. 
     The reception cylinder  263  has a substantially columnar shape extending in the left-right direction, and protrudes toward the left side from a circumferential edge of the toner return hole  262  of the accommodation portion side wall  280 . A left end of the reception cylinder  263  is closed. 
     The reception cylinder  263  includes a toner return reception hole  264 . The toner return reception hole  264  is disposed at a rear upper end of the reception cylinder  263  as shown in  FIG. 17B , and penetrates through the reception cylinder  263  in a direction which connects the front lower side to the rear upper side. 
     The first shutter  255  has a substantially cylindrical shape extending in the left-right direction, and is fitted in the left end of the auger accommodation cylinder  257  from outside in a radial direction. An inner diameter of the first shutter  255  is substantially the same as an outer diameter of the auger accommodation cylinder  257 . 
     The first shutter  255  includes a first shutter opening  265 . The first shutter opening  265  penetrates through the first shutter  255  in the radial direction. The first shutter  255  is rotated along an outer circumferential surface of the auger accommodation cylinder  257  between a closed position where the toner ejection hole  260  is closed, and an open position where, as shown in  FIG. 18B , the toner ejection hole  260  is opened when the first shutter opening  265  allows the toner ejection hole  260  and the auger accommodation cylinder  257  to communicate with each other in the radial direction. The first shutter  255  is disposed at the closed position at the normal time. 
     As shown in  FIG. 17A , the second shutter  256  has a substantially cylindrical shape extending in the left-right direction, and is fitted in the reception cylinder  263  from outside in the radial direction. An inner diameter of the second shutter  256  is substantially the same as an outer diameter of the reception cylinder  263 . 
     The second shutter  256  includes a second shutter opening  266  as shown in  FIG. 17B . The second shutter opening  266  penetrates through the second shutter  256  in the radial direction. Further, the second shutter  256  is rotated along an outer circumferential surface of the reception cylinder  263  between a closed position where the toner return reception hole  264  is closed, and an open position where, as shown in  FIG. 18B , the second shutter opening  266  allows the toner return reception hole  264  and the reception cylinder  263  to communicate with each other in the radial direction. The second shutter  256  is disposed at the closed position at the normal time. 
     The auger member  252  is disposed inside the auger accommodation cylinder  257  as shown in  FIG. 17A . The auger member  252  includes an auger shaft portion  282  and a screw portion  283 . 
     The auger shaft portion  282  has a columnar shape extending in the left-right direction. The screw portion  283  is entirely disposed on a circumferential surface of the auger shaft portion  282  and extends in a helical shape in the left-right direction. The auger member  252  is rotatably supported at the auger accommodation cylinder  257  while both left and right ends of the auger shaft portion  282  are supported at both left and right ends of the auger accommodation cylinder  257 . 
     The agitator  253  is disposed on the front lower side of the toner passing hole  261  at the rear end in the toner accommodation portion  258  as shown in  FIG. 16 . The agitator  253  transports toner in the toner accommodation portion  258  to the toner passing hole  261 , and includes an agitator shaft  285  and an agitation film  286 . 
     The agitator shaft  285  has a substantially columnar shape extending in the left-right direction as shown in  FIG. 17A . The agitation film  286  extends outward in the radial direction of the agitator shaft  285  from the agitator shaft  285 . The agitator  253  is rotatably supported at the toner accommodation portion  258  while both left and right ends of the agitator shaft  285  are supported at the rear ends of the pair of accommodation portion side walls  280 . 
     The agitation member  254  is disposed on the front side of the agitator  253  in the toner accommodation portion  258 . The agitation member  254  agitates toner in the toner accommodation portion  258  and transports the toner rearward. 
     The agitation member  254  includes a swing shaft  268 , a first agitation portion  269 , and a second agitation portion  270 . 
     The swing shaft  268  has a substantially columnar shape extending in the left-right direction as shown in  FIG. 17A . Each of both left and right ends of the swing shaft  268  is bent in a substantially crank shape. 
     The first agitation portion  269  has a substantially ladder shape in a plan view, and is curved toward the front upper side in a side view as shown in  FIG. 16 . A front end of the first agitation portion  269  is supported at the swing shaft  268  so as to be relatively rotated. 
     The second agitation portion  270  has a substantially ladder shape in a plan view as shown in  FIG. 17A , and extends in the front-rear direction in a side view as shown in  FIG. 16 . A front end of the second agitation portion  270  is connected to a rear end of the first agitation portion  269  so as to be relatively rotated. 
     The agitation member  254  is supported at the toner accommodation portion  258  while both left and right ends of the swing shaft  268  are supported at the front ends of the pair of accommodation portion side walls  280 . 
     The toner cartridge  202  is mounted to the process cartridge  201 . In order to mount the toner cartridge  202  to the process cartridge  201 , a operator, as shown in  FIG. 18B , assembles the toner cartridge  202  in the process cartridge  201  from the front upper side so that the left end of the auger accommodation cylinder  257  is received by the first reception portion  235  and the reception cylinder  263  is received by the second reception portion  240 . 
     In the above-described manner, as shown in  FIG. 16 , the toner cartridge  202  is mounted to the process cartridge  201 , and thus the process unit  200  is completed. At this time, the auger cylinder reception portion  210  supports the auger accommodation cylinder  257 , and the toner accommodation receiving portion  211  supports the toner accommodation portion  258 . 
     The process unit  200  is mounted to the main body casing  2  by the operator. When the process unit  200  is mounted to the main body casing  2 , as shown in  FIG. 15 , the operator swings the flat bed scanner  40  in the counterclockwise direction in a left side view, and also disposes the top cover  77  at the open position. Next, the operator inserts the process unit  200  into the main body casing  2  through the process opening  75 . 
     In the above-described manner, the process unit  200  is disposed inside the main body casing  2  and is located at the internal position as shown in  FIG. 13 . 
     In a state where the process unit  200  is located at the internal position, the rear end of the roller accommodation portion  122  of the process cartridge  201  is disposed inside the recess portion  104  of the reception part  105 , and the front reception portion  213  of the process cartridge  201  is disposed on the rear upper side with respect to the guide wall  71  and the inclined wall  70  of the mounting/removing guide wall  67  with an interval therebetween. 
     Therefore, the front end of the toner cartridge  202 , specifically, the front end of the toner accommodation portion  258  overlaps the rear part of the scanner unit  16  when projected in the upper-lower direction. 
     Next, the operator moves the first shutter  255  from the closed position to the open position as shown in  FIG. 18B . Thus, the toner ejection hole  260 , the first shutter opening  265 , and the toner supply reception hole  237  communicate with each other in the radial direction of the auger accommodation cylinder  257 . 
     Further, the operator moves the second shutter  256  from the closed position to the open position, and also moves the reception portion shutter  244  from the closed position to the open position. Thus, the toner discharge hole  245 , the second shutter opening  266 , and the toner return reception hole  264  communicate with each other in the radial direction of the reception cylinder  263 . 
     Successively, as shown in  FIG. 13 , the operator moves the top cover  77  from the open position to the closed position, and also swings the flat bed scanner  40  in the clockwise direction in a left side view. 
     In the above-described manner, the mounting of the process unit  200  to the main body casing  2  is completed. 
     In order to remove the process unit  200  from the main body casing  2 , procedures are performed in a reverse order to the above-described mounting operation. 
     (6) Image Forming Operation in Third Illustrative Embodiment 
     In an image forming operation of the printer  1 , the scanner unit  16  emits the laser beam L toward the surface of the photosensitive drum  20  in the rear lower direction under the control of a controller (not shown) as shown in  FIG. 13 . The laser beam L passes through the laser passing hole  124  of the process front wall  207 , then pass under the rear reception portion  212  of the toner accommodation receiving portion  211 , and exposes the front circumferential surface of the drum body  132  of the photosensitive drum  20 . 
     That is, the toner cartridge  202  is disposed on the upper side with respect to a light path of the laser beam L, and the developing unit  205  is disposed on the lower side with respect to the light path of the laser beam L. 
     The laser beam L passes between the pair of process side walls  206  in the left-right direction as shown in  FIG. 18A . That is, the laser beam L passes through the opposite side to the transport unit  230  with respect to the left process side wall  206 . That is, the transport unit  230  is disposed on the further left side than the laser beam L with an interval therebetween. 
     In the image forming operation, toner is circulated between the toner cartridge  202  and the developing unit  205 . 
     In a toner circulation operation, as shown in  FIG. 13 , if the agitation member  254  is rotated, the agitation member  254  agitates the toner in the toner accommodation portion  258  and causes the toner to flow rearward. Then, the agitator  253  is rotated so as to transport the toner toward the toner passing hole  261 . 
     At this time, the toner is supplied to the auger accommodation cylinder  257  from the toner accommodation portion  258  via the toner passing hole  261  as shown in  FIG. 17A . Then, the auger member  252  is rotated so that the toner supplied into the auger accommodation cylinder  257  is transported toward the left side. 
     Then, as shown in  FIG. 18B , the toner reaches the left end of the auger accommodation cylinder  257 , and falls into the supply toner transport chamber  276  due to the gravity via the toner ejection hole  260 , the first shutter opening  265 , and the toner supply reception hole  237 . Accordingly, the toner flows up to the lower end of the supply toner transport chamber  276 . 
     Next, the first auger  218  is rotated so as to transport the toner having reaching the lower end of the supply toner transport chamber  276  toward the right side. Thus, the toner is moved from the lower end of the supply toner transport chamber  276  to the inside of the first auger accommodation portion  222  of the developing frame  220  via the toner supply port  216 . 
     Further, as shown in  FIG. 19 , the first auger  218  is rotated so as to transport the toner in the first auger accommodation portion  222  toward the right side. At this time, some portion of the toner transported by the first auger  218  is supplied to the supply roller  27  via the toner opening  227  as shown in  FIG. 13 . 
     Then, in the same manner as in the image forming operation, the supply roller  27  supplies the toner to the developing roller  26 , and the developing roller  26  supplies the toner to an electrostatic latent image on the circumferential surface of the drum body  132 . 
     On the other hand, the toner which is transported to the right end of the first auger accommodation portion  222  due to the rotation of the first auger  218  is moved from the first auger accommodation portion  222  to the second auger accommodation portion  223  via the communication hole  228  as shown in  FIGS. 16 and 19 . 
     Then, the second auger  219  is rotated so as to transport the toner in the second auger accommodation portion  223  toward the left side. Then, as shown in  FIG. 18B , the toner is moved from the second auger accommodation portion  223  to the tonner return transport chamber  277  via the toner return hole  217 . 
     Next, the transport belt  243  is circumferentially moved so as to transport the toner in the tonner return transport chamber  277  toward the front upper side. Then, the toner reaches the upper end of the tonner return transport chamber  277 . Accordingly, the toner falls into the reception cylinder  263  from the tonner return transport chamber  277  via the toner discharge hole  245 , the second shutter opening  266 , and the toner return reception hole  264 . 
     Next, as shown in  FIG. 17A , the toner is returned to the toner accommodation portion  258  from the reception cylinder  263  via the toner return hole  262 . 
     In the above-described manner, the toner circulation operation is performed. The toner circulation operation is continuously performed in the image forming operation of the printer  1 . 
     Incidentally, as shown in  FIG. 13 , a sheet P accommodated in the sheet feed cassette  7  is transported from the sheet feed cassette  7  toward the contact point N between the drum body  132  and the transfer roller  21  and passes through the contact point N in the same manner as in the image forming operation. The sheet P on which a toner image is formed passes between the heating roller  30  and the pressing roller  31 , and is then discharged to the sheet discharge tray  35  by the pair of sheet discharge rollers  34 . 
     (7) Removing Operation of Toner Cartridge from Main Body Casing 
     The toner cartridge  202  can be removed from the process cartridge  201  mounted in the main body casing  2 . 
     In order to remove the toner cartridge  202  from the process cartridge  201  mounted in the main body casing  2 , first, the operator rotates the top cover  77  in the counterclockwise direction in a left side view from the closed position, so as to secure a space through which the toner cartridge  202  passes between the cover body  79  and the mounting/removing guide wall  67 . 
     Next, as shown in  FIG. 17B , the operator moves the first shutter  255  from the open position to the closed position, and also moves the second shutter  256  from the open position to the closed position. 
     Then, as shown in  FIG. 14 , the operator pulls out the toner cartridge  202  toward the front upper side through the space between the cover body  79  and the mounting/removing guide wall  67 . 
     Thus, the toner cartridge  202  is removed from the process cartridge  201  mounted in the main body casing  2 . 
     (8) Operations and Effects of Third Illustrative Embodiment 
     (8-1) The toner cartridge  202  accommodates the toner supplied to the developing frame  220  as shown in  FIG. 13 . Therefore, it is possible to increase an amount of toner accommodated in the process unit  200 . 
     Further, the toner cartridge  202  is disposed on the upper side with respect to the light path of the laser beam L. Therefore, it is possible to prevent the toner cartridge  202  from interfering with exposure of the photosensitive drum  20  to the laser beam L. 
     As a result, it is possible to increase an amount of toner accommodated in the process unit  200  and to reliably expose the photosensitive drum  20 . 
     Further, the toner accommodation portion  258  of the toner cartridge  202  is disposed further forward than the photosensitive drum  20 , and the heating roller  30  of the fixing unit  17  is disposed further rearward than the photosensitive drum  20 . Therefore, the heating roller  30  and the toner accommodation portion  258  are disposed with an interval therebetween in the front-rear direction. As a result, heat generated when the fixing unit  17  fixes a toner image onto a sheet P can be prevented from influencing toner in the toner accommodation portion  258 . 
     (8-2) The developing unit  205  is disposed on the lower side with respect to the light path of the laser beam L as shown in  FIG. 13 . Therefore, it is possible to prevent the developing unit  205  from interfering with exposure of the photosensitive drum  20  by the laser beam L. The developing unit  205  is disposed on an opposite side to the toner cartridge  202  with respect to the light path of the laser beam L, and thus it is possible to ensure an efficient arrangement of the developing unit  205  and the toner cartridge  202 . 
     (8-3) The toner cartridge  202  is removably mounted to the process cartridge  201  as shown in  FIG. 14 . Therefore, it is possible to improve maintenance property of the toner cartridge  202 . 
     (8-4) The toner supply transport portion  233  transports toner from the toner cartridge  202  to the developing unit  205  as shown in  FIG. 18B . Therefore, it is possible to reliably transport the toner from the toner cartridge  202  to the developing frame  220 . Further, the toner supply transport portion  233  is disposed on the left side with respect to the light path of the laser beam L with an interval therebetween as shown in  FIG. 18A . Therefore, it is possible to prevent the toner supply transport portion  233  from interfering with exposure of the photosensitive drum  20  by the laser beam L. 
     As a result, it is possible to reliably transport the toner from the toner cartridge  202  to the developing frame  220  and also to reliably expose the photosensitive drum  20 . 
     Also, in the third illustrative embodiment, it is possible to achieve the same operations and effects as in the first illustrative embodiment. 
     Incidentally, in the third illustrative embodiment, the process unit  200  is an example of a process unit; the toner cartridge  202  is an example of a second developer accommodation portion; the developing frame  220  is an example of a first developer accommodation portion; and the toner supply transport portion  233  is an example of a developer transport portion. 
     10. Fourth Illustrative Embodiment 
     Next, with reference to  FIG. 20 , a fourth illustrative embodiment of the printer  1  will be described. In the fourth illustrative embodiment, the same members as in the first illustrative embodiment are given the same reference numerals, and description thereof will be omitted. 
     (1) Details of Process Cartridge of Fourth Illustrative Embodiment 
     The process cartridge  15  includes a charging roller  300  and a cleaning unit  303 . 
     The charging roller  300  has a substantially columnar shape extending in the left-right direction, and is disposed on the front upper side with respect to the photosensitive drum  20 . A rear lower end of the charging roller  300  is in contact with a front upper end of the photosensitive drum  20 . 
     The cleaning unit  303  removes attached substances such as remaining toner attached onto the photosensitive drum  20 . The cleaning unit  303  is disposed on the upper side of the photosensitive drum  20  and the developing cartridge  19 . The cleaning unit  303  includes a cleaner frame  304 , a cleaning blade  305 , and a sheet member  306 . 
     The cleaner frame  304  is disposed on the upper side of the developing cartridge  19  and the photosensitive drum  20 . The cleaner frame  304  has a substantially box shape extending in the front-rear direction. The cleaner frame  304  includes a reservoir  307  and a collecting portion  308 . 
     The reservoir  307  is a front part of the cleaner frame  304 , and is disposed on the front upper side of the charging roller  300 . 
     The collecting portion  308  is a rear part of the cleaner frame  304 , and is disposed on the upper side of the charging roller  300  and the photosensitive drum  20 . An upper surface of the collecting portion  308  is connected to an upper surface of the reservoir  307  to have a flat surface. That is, the collecting portion  308  is disposed parallel to the reservoir  307  in the front-rear direction, and communicates with the reservoir  307 . A dimension of the collecting portion  308  in the upper-lower direction is smaller than a dimension of the reservoir  307  in the upper-lower direction. The collecting portion  308  includes a cleaner opening  309 . 
     The cleaner opening  309  is disposed at a substantially center in the front-rear direction in a lower wall of the collecting portion  308 , and penetrates through the lower wall of the collecting portion  308  in the upper-lower direction. The cleaner opening  309  extends in the entire lower wall of the collecting portion  308  in the left-right direction. 
     The cleaning blade  305  is disposed on the upper side of the photosensitive drum  20  and the lower side of the collecting portion  308 . That is, the reservoir  307  is disposed further forward than the cleaning blade  305 . The cleaning blade  305  has a plate shape which has a thickness in the upper-lower direction and extends in the left-right direction. A front end of the cleaning blade  305  is fixed to a front circumferential edge of the cleaner opening  309  on a lower surface of the lower wall of the collecting portion  308 . A rear end of the cleaning blade  305  faces a half of the cleaner opening  309  on the front side. The rear end of the cleaning blade  305  is in contact with the upper end of the photosensitive drum  20 , that is, the circumferential surface of the drum body  132 . 
     The sheet member  306  prevents attached substances in the cleaner frame  304  which are removed from the photosensitive drum  20  from leaking out from the cleaner opening  309 . The sheet member  306  is disposed at a lower end of the collecting portion  308  and on the rear side of the cleaning blade  305 . The sheet member  306  is made of a flexible sheet material. A rear end of the sheet member  306  is fixed to a rear circumferential edge of the cleaner opening  309  on the lower surface of the lower wall of the collecting portion  308 . A front end of the sheet member  306  faces a half of the cleaner opening  309  on the rear side. A front end of the sheet member  306  is in contact with the upper end of the photosensitive drum  20 . 
     When an image forming operation is started and the photosensitive drum  20  is rotated, the cleaning blade  305  of the cleaning unit  303  scrapes attached substances such as remaining toner attached to the photosensitive drum  20  so that the attached substances are collected into the collecting portion  308 . The attached substances collected in the collecting portion  308  are stored in the reservoir  307 . That is, the reservoir  307  stores attached substances removed from the surface of the photosensitive drum  20  by the cleaning blade  305 . 
     In the image forming operation, the scanner unit  16  emits a laser beam L toward the surface of the photosensitive drum  20  in the rear lower direction. The laser beam L passes over the developing cartridge  19  and under the cleaning unit  303 , that is, passes between the developing cartridge  19  and the cleaning unit  303 , and eposes the circumferential surface of the photosensitive drum  20 . That is, the cleaning unit  303  is disposed on the upper side with respect to the light path of the laser beam L. 
     (2) Operations and Effects of Process Cartridge of Fourth Illustrative Embodiment 
     (2-1) The cleaning unit  303  cleans attached substances from the photosensitive drum  20 . Therefore, it is possible to minimize the occurrence of poor image formation due to the attached substances on the photosensitive drum  20 . Further, the cleaning unit  303  is disposed on the upper side with respect to the light path of the laser beam L. As a result, it is possible to prevent the cleaning unit  303  from interfering with exposure of the photosensitive drum  20  by the laser beam L. 
     (2-2) The cleaning blade  305  of the cleaning unit  303  is in contact with the circumferential surface of the photosensitive drum  20 . Therefore, it is possible to reliably clean attached substances from the photosensitive drum  20 . Further, attached substances scraped by the cleaning blade  305  are stored in the reservoir  307  of the cleaner frame  304 . 
     Since the reservoir  307  is disposed on the front side with respect to the cleaning blade  305 , the fixing unit  17  and the photosensitive drum  20  can be disposed to be close to each other even if a size of the reservoir  307  is increased. Therefore, it is possible to reliably transport a sheet P from the photosensitive drum  20  to the fixing unit  17 . 
     Further, the reservoir  307  is disposed further forward than the photosensitive drum  20 , and the heating roller  30  of the fixing unit  17  is disposed further rearward than the photosensitive drum  20 . Therefore, the heating roller  30  and the reservoir  307  are disposed with an interval therebetween in the front-rear direction. As a result, heat generated when the fixing unit  17  fixes a toner image onto a sheet P can be prevented from influencing attached substances in the reservoir  307 . 
     Also, in the fourth illustrative embodiment, it is possible to achieve the same operations and effects as in the first illustrative embodiment. 
     Incidentally, in the fourth illustrative embodiment, the cleaning unit  303  is an example of a cleaning unit; the cleaning blade  305  is an example of a blade; and the reservoir  307  is an example of a reservoir. 
     11. Fifth Illustrative Embodiment 
     Next, with reference to  FIG. 21 , a fifth illustrative embodiment of the printer  1  will be described. In the fifth illustrative embodiment, the same members as in the first illustrative embodiment are given the same reference numerals, and description thereof will be omitted. Further, among operations in the fifth illustrative embodiment, the same operation in the first illustrative embodiment will not be repeated. 
     In the fifth illustrative embodiment of the present invention, the sheet guide section  6  includes a sixth sheet guide  311 . 
     Although described later in detail, the sixth sheet guide  311  guides transport of a sheet P so that the sheet P reaches the inclined guide  99  from the sheet discharge rollers  34  in a duplex printing operation. 
     The sixth sheet guide  311  connects the downstream part  96  of the first sheet guide  88  to the concave portion  106  of the fourth sheet guide  91 , and includes a first guide connection portion  312 , a middle portion  313 , and a fourth guide connection portion  314 . 
     The first guide connection portion  312  has a substantially C shape which is opened rearward in a side view. An upper end of the first guide connection portion  312  is connected to a substantially center of the lower inclined guide  99  in the front-rear direction. Thus, the first guide connection portion  312  communicates with the pair of inclined guides  99 . 
     The middle portion  313  is connected to the lower end of the first guide connection portion  312 , and extends rearward. The middle portion  313  is disposed to be adjacent to the second sheet guide  89  on the lower side. 
     The fourth guide connection portion  314  is disposed at a rear end of the middle portion  313 , and has a substantially C shape which is opened forward in a side view. A lower end of the fourth guide connection portion  314  is connected to the rear end of the middle portion  313 , and an upper end of the fourth guide connection portion  314  is connected to the rear end of the fourth sheet guide  91 . Thus, the fourth guide connection portion  314  communicates with the middle portion  313 . Further, the fourth sheet guide  91  includes a sheet passing hole  316  and a curved plate  315 . 
     The sheet passing hole  316  is disposed on the front side of the upper end of the fourth guide connection portion  314  at the rear end of the fourth sheet guide  91 . The sheet passing hole  316  has a shape and a size which allow the sheet P to pass through the sheet passing hole  316 , and penetrates through the rear end of the fourth sheet guide  91  in the front-rear direction so as to communicate with the concave portion  106 . Thus, the fourth guide connection portion  314  communicates with the concave portion  106  of the fourth sheet guide  91  via the sheet passing hole  316 . 
     The curved plate  315  has a substantially C plate shape which is opened toward the front lower side in a side view, and is curved along the concave portion  106 . The curved plate  315  is disposed on the lower side with respect to the concave portion  106  with an interval therebetween. Further, a rear end of the curved plate  315  is disposed on the upper side of the front guide rollers  33 , and a front end of the curved plate  315  is disposed on the rear upper side of the rear sheet discharge rollers  34 . 
     The pair of sheet discharge rollers  34  switches its rotation between a first rotation in which the sheet P is discharged toward the sheet discharge tray  35  and a second rotation in which the sheet P is transported toward the sheet passing hole  316 . 
     In the fifth illustrative embodiment, when images are formed on both sides of the sheet P, first, a toner image is formed on one surface of the sheet P in the same manner as in the above-described image forming operation. The sheet P is transported toward the sheet discharge tray  35  until a trailing end of the sheet P in the transport direction is located on the front of the sheet passing hole  316  of the fourth sheet guide  91 . 
     Then, if the trailing end of the sheet P in the transport direction is disposed on the front side of the sheet passing hole  316  of the fourth sheet guide  91 , the pair of sheet discharge rollers  34  switches its rotation from the first rotation to the second rotation. Thus, the pair of sheet discharge rollers  34  reverses the transport direction of the sheet P so as to transport the sheet P rearward. 
     Then, the sheet P enters the fourth guide connection portion  314  of the sixth sheet guide  311  through the sheet passing hole  316 . The fourth guide connection portion  314 , the middle portion  313 , and the first guide connection portion  312  sequentially guide the sheet P. 
     Thus, the sheet P reaches between the pair of inclined guides  99 , and is supplied between the second transport rollers  101  again. The pair of second transport rollers  101  is rotated so as to supply the sheet P to the contact point N between the drum body  132  and the transfer roller  21 . 
     Further, when the sheet P passes through the contact point N, the transfer roller  21  transfers a toner image carried on the circumferential surface of the drum body  132  onto the other surface of the sheet P. Accordingly, the toner images are formed on both sides of the sheet P. 
     Then, in the same manner as the above-described image forming operation, the toner image is fixed onto the sheet P by the fixing unit  17 , and then the sheet P is discharged to the sheet discharge tray  35  through the first rotation of the pair of sheet discharge rollers  34 . 
     According to the fifth illustrative embodiment, the sheet guide section  6  includes the sixth sheet guide  311 , and thus toner images can be formed on both sides of the sheet P. 
     Also, in the fifth illustrative embodiment, it is possible to achieve the same operations and effects as in the first illustrative embodiment. 
     12. Sixth Illustrative Embodiment 
     Next, with reference to  FIG. 22 , a sixth illustrative embodiment of the printer  1  will be described. In the sixth illustrative embodiment, the same members as in the first illustrative embodiment are given the same reference numerals, and description thereof will be omitted. 
     In the sixth illustrative embodiment of the present invention, the second sheet guide  89  includes a cartridge lift  331 . 
     The cartridge lift  331  moves the process cartridge  15  between the internal position and the extraction position in interlocking with a movement of the top cover  77  between the closed position and the open position. 
     The cartridge lift  331  includes a lift shaft  333 , lift plates  334 , and a lift spring  335 . 
     The lift shaft  333  has a substantially columnar shape extending in the left-right direction, and is rotatably supported on the lower side of the guide protrusion  103  in the second sheet guide  89 . 
     The lift plates  334  are respectively disposed at both left and right ends of the lift shaft  333 . The lift plates  334 , which have a plate shape, extend outward in the radial direction from the lift shaft  333 , and are then bent so as to be inclined in the counterclockwise direction in a left side view. A dimension between the two lift plates  334  in the left-right direction is larger than a dimension of the sheet P in the left-right direction. 
     The lift spring  335  is a compression spring extending in the upper-lower direction, and is disposed between the lift plates  334  and the second sheet guide  89 . 
     The cartridge lift  331  can swing between a compression position indicated by a broken line where the process cartridge  15  is located at the internal position and an extended position indicated by a solid line where the process cartridge  15  is located at the extraction position, with the lift shaft  333  as a fulcrum. 
     When the top cover  77  is located at the closed position, the cover body  79  comes into contact with the upper end of the handle portion  133  of the process cartridge  15  so as to press the process cartridge  15  downward. Thus, the cartridge lift  331  is located at the compression position, and the process cartridge  15  is located at the internal position. 
     In a state where the cartridge lift  331  is located at the compression position, the lift spring  335  is compressed in the upper-lower direction, and the lift plate  334  is disposed so as to extend forward from the lift shaft  333 . At this time, an upper surface at a front end of the lift plate  334  is in contact with a lower surface at both ends of the contact portion  117  of the process cartridge  15  in the left-right direction. 
     If the top cover  77  is moved from the closed position to the open position, the contact between the cover body  79  and the upper end of the handle portion  133  of the process cartridge  15  is released. 
     Accordingly, the lift plate  334  is swung in the counterclockwise direction in a left side view by a biasing force of the lift spring  335 , and thus the cartridge lift  331  is moved from the compression position to the extended position. At this time, the lift plate  334  is disposed so as to extend from the lift shaft  333  toward the front upper side. Thus, the contact portion  117  of the drum front wall  111  is brought into contact with the front end of the lift plate  334  so as to be biased upward. 
     Then, the process cartridge  15  is moved from the internal position to the extraction position. Also, the handle  115  is moved from the accommodation position to the ejection position by the gravity in interlocking with the movement of the process cartridge  15  from the internal position to the extraction position in the same manner as described above. 
     Further, when the top cover  77  is moved from the open position to the closed position, the cover body  79  is brought into contact with the handle portion  133  of the process cartridge  15 , and the process cartridge  15  is pressed downward according to the movement of the top cover  77 . 
     Therefore, the front end of the lift plate  334  is brought into contact with the lower surface of the contact portion  117  of the process cartridge  15 , and thus the cartridge lift  331  is swung in the clockwise direction in a left side view while resisting the biasing force of the lift spring  335 , so as to be located at the compression position. 
     Accordingly, the process cartridge  15  is moved from the extraction position to the internal position. The handle  115  is moved from the ejection position to the accommodation position in interlocking with the movement of the process cartridge  15  from the extraction position to the internal position. 
     Incidentally, in the sixth illustrative embodiment, the cartridge lift  331  is an example of an interlocking mechanism. 
     Also, in the sixth illustrative embodiment, it is possible to achieve the same operations and effects as in the first illustrative embodiment. 
     13. Seventh Illustrative Embodiment 
     Next, with reference to  FIG. 23A , a seventh illustrative embodiment of the printer  1  will be described. In the seventh illustrative embodiment, the same members as in the first illustrative embodiment are given the same reference numerals, and description thereof will be omitted. 
     The developing cartridge  19  includes a brush roller  346  and a supply member  347 . 
     The brush roller  346  includes a brush portion  340 . 
     The brush portion  340  is formed by a pile of nylon, polyester, or the like, and is disposed on a circumferential surface of the brush roller  346 . The brush portion  340  is in contact with the photosensitive drum  20 . 
     The supply member  347  includes a supply shaft  342 , a pair of disc portions  343 , and a plurality of paddle portions  344 . 
     The supply shaft  342  has a substantially columnar shape extending in the left-right direction. Both left and right ends of the supply shaft  342  are rotatably supported at the developing frame  25 . 
     The pair of disc portions  343  are disposed with an interval therebetween in the left-right direction. The disc portions  343  have a substantially circular plate shape in a side view. 
     The disc portions  343  are respectively disposed at both left and right ends of the supply shaft  342  so as to share a center axis line with the supply shaft  342 . The disc portions  343  are disposed inward in the left-right direction with respect to the corresponding developing side walls  137  with an interval therebetween. 
     Each of the plurality of paddle portions  344  has a plate shape extending in the left-right direction, and is disposed so as to connect the pair of disc portions  343  to each other. Each of the paddle portions  344  extends so as to intersect the radial direction of the supply shaft  342  in a side view. Thus, the pair of disc portions  343  and the plurality of paddle portions  344  substantially configure an impeller. 
     The supply member  347  is rotatably supported at the developing frame  25  while both left and right ends of the supply shaft  342  are supported at the pair of developing side walls  137 . 
     In an image forming operation, the supply member  347  sweeps out toner which is supplied from the agitator  142 , with the plurality of paddle portions  344 , so as to supply the toner to the brush roller  346 . The layer thickness regulation blade  28  scrapes off the toner carried on the brush portion  340  of the brush roller  346  through a rotation of the brush roller  346 . Thus, the brush roller  346  carries a constant amount of toner. 
     Also, in the above-described manner, a toner image can be formed on the sheet P in the same manner as in the first illustrative embodiment. Further, also in the seventh illustrative embodiment, it is possible to achieve the same operations and effects as in the first illustrative embodiment. 
     Incidentally, in the seventh illustrative embodiment, the brush roller  346  is an example of a developer carrier. 
     14. Eighth Illustrative Embodiment 
     Next, with reference to  FIG. 23B , an eighth illustrative embodiment of the printer  1  will be described. In the eighth illustrative embodiment, the same members as in the first illustrative embodiment are given the same reference numerals, and description thereof will be omitted. 
     The drum cartridge  18  of the process cartridge  15  includes a handle spring  350 . 
     The handle spring  350  is a compression spring extending in a direction which connects the front lower side to the rear upper side, and is disposed between each of the pair of connection portions  128  and the front wall body  114  of the drum front wall  111 . 
     Thus, the handle  115  is biased toward the front lower side at the normal time. 
     Therefore, the handle  115  is reliably moved from the accommodation position to the ejection position by a biasing force of the handle spring  350 . 
     Also, in the eighth illustrative embodiment, it is possible to achieve the same operations and effects as in the first illustrative embodiment. 
     While the present invention has been shown and described with reference to certain illustrative embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. 
     For example, the above-described first to eighth illustrative embodiments may be arbitrary combined.