Patent Publication Number: US-9422123-B2

Title: Sheet cassette, feeder, and image forming apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a sheet cassette in which a plurality of sheets are loaded, a feeder, and an image forming apparatus. 
     BACKGROUND ART 
     A sheet feed cassette disclosed in Patent Literature 1 includes a cassette main body and a cassette extendable section. The size of the sheet feed cassette is adjusted by sliding in and out the cassette extendable section according to the size of sheets. 
     The sheet feed cassette includes a lock mechanism. The lock mechanism includes an engagement hole and a lock button. The engagement hole is provided in the cassette main body. The lock button is provided in the cassette extendable section. 
     The lock button is in engagement with the engagement hole in a locked state. Pushing down the lock button releases the lock button from the engagement hole. Thus, the locked state of the cassette main body and the cassette extendable section is released. As a result, the cassette extendable section becomes slidable relative to the cassette main body. 
     CITATION LIST 
     Patent Literature 
     [Patent Literature 1] 
     Japanese Patent Application Laid-Open Publication No. 2001-97561 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, the sheet feed cassette disclosed in Patent Literature 1 has the following problem. That is, since manipulating the lock button itself does not slide the cassette extendable section, a user is required to grab a certain part of the cassette extendable section and slide in or out the cassette extendable portion. Accordingly, manipulation of at least two parts is needed in order to release the locked state and slide in or out the cassette extendable section. Furthermore, once sheets are loaded, the locked state of the cassette main body (main cassette) and the cassette extendable section (sliding cassette) is generally required to be hard to release. 
     In view of the above-described problem, the present invention has been made to provide: a sheet cassette whose size is adjustable by simple manipulation and which is capable of restricting release of a locked state of a main cassette and a sliding cassette after loading of sheets; a feeder; and an image forming apparatus. 
     Solution to Problem 
     According to a first aspect of the present invention, a sheet cassette is to be loaded with a plurality of sheets and is adjustable in size. The sheet cassette includes a first sheet accommodation section, a second sheet accommodation section, and a restricting section. The first sheet accommodation section has a first bottom on which the plurality of sheets are loaded. The second sheet accommodation section has a second bottom on which the plurality of sheets are loaded. The second sheet accommodation section is attached to the first sheet accommodation section so as to be slidable between a retracted position where the second sheet accommodation section is retracted in the first sheet accommodation section and an extended position where the second sheet accommodation section is drawn out from the first sheet accommodation section in an extending direction. The restricting section restricts sliding of the second sheet accommodation section in the retracted position. The restricting section includes a lever section, a first engagement section, and a second engagement section. The lever section extends from the second bottom in the extending direction and has a distal end portion in the extending direction that is swingable in upward and downward directions. The first engagement section is disposed in the first bottom. The second engagement section is disposed in the lever section and is engageable with the first engagement section. The lever section is shiftable between a first engaged position, a second engaged position, and a disengaged position while the second sheet accommodation section is in the retracted position. The first engaged position is a position where no sheets are loaded on the second bottom, the distal end portion protrudes from a sheet loading surface of the second bottom, and the first engagement section and the second engagement section are in engagement. The second engaged position is a position where the distal end portion is pushed down out of the first engaged position in accordance with a number of sheets loaded on the second bottom, and the first engagement section and the second engagement section are in engagement. The disengaged position is a position where the lever section is lifted out of the first engaged position, and thus the engagement between the first engagement section and the second engagement section is released. Strength of the engagement between the first engagement section and the second engagement section is larger when the lever section is in the first engaged position than when the lever section is in the second engaged position. 
     According to a second aspect of the present invention, a feeder includes the sheet cassette according to the first aspect and a feeding section. The feeding section feeds a sheet from the sheets in the sheet cassette. 
     According to a third aspect of the present invention, an image forming apparatus includes the feeder according to the second aspect and an image forming section. The image forming section forms an image on the sheet fed by the feeder. 
     Advantageous Effects of Invention 
     According to the present invention, a user can slide the second sheet accommodation section by lifting the lever section to release the engagement, and subsequently pulling the lever section in a direction away from the first sheet accommodation section or pushing the lever section in a direction toward the first sheet accommodation section. That is, the releasing of the engagement and the sliding can be performed by a series of manipulation actions on the lever section. Once sheets are loaded, the distal end portion of the lever section is pushed down and the lever section is shifted from the first engaged position to the second engaged position. As a result, strength of the engagement between the first engagement section and the second engagement section is increased. It is therefore possible to adjust the size of the sheet cassette by simple manipulation and restrict release of a locked state of the main cassette and the sliding cassette after loading of sheets. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a sheet cassette according to a first embodiment of the present invention. 
         FIG. 2  is an enlarged perspective view of a first restricting section of the sheet cassette according to the first embodiment of the present invention. 
         FIG. 3  is a cross-sectional view illustrating the first restricting section of the sheet cassette according to the first embodiment of the present invention (first engaged position). 
         FIG. 4  is a cross-sectional view illustrating the first restricting section of the sheet cassette according to the first embodiment of the present invention (disengaged position). 
         FIG. 5  is a cross-sectional view illustrating a second restricting section of the sheet cassette according to the first embodiment of the present invention. 
         FIG. 6  is a cross-sectional view illustrating the first restricting section of the sheet cassette according to the first embodiment of the present invention (second engaged position). 
         FIG. 7  is a cross-sectional view illustrating a first restricting section of a sheet cassette according to a second embodiment of the present invention (first engaged position). 
         FIG. 8  is a cross-sectional view illustrating the first restricting section of the sheet cassette according to the second embodiment of the present invention (second engaged position). 
         FIG. 9  is a cross-sectional view illustrating the first restricting section of the sheet cassette according to the second embodiment of the present invention (disengaged position). 
         FIG. 10A  is a cross-sectional view illustrating a first restricting section of a sheet cassette according to a third embodiment of the present invention. 
         FIG. 10B  is a schematic view illustrating a rack of the first restricting section of the sheet cassette according to the third embodiment of the present invention. 
         FIG. 11  is a schematic cross-sectional view for illustrating an overview of an image forming apparatus according to a fourth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that elements in the drawings that are the same or equivalent are labelled using the same reference signs and description thereof is not repeated. 
     First Embodiment 
     Basic Principle 
     The basic principle of a sheet cassette  1  according to the first embodiment of the present invention will be described with reference to  FIGS. 1 to 6 .  FIG. 1  is a perspective view of the sheet cassette  1 . A plurality of sheets (not shown) are loaded in the sheet cassette  1  which is adjustable in size. The sheet cassette  1  includes a main cassette  3  (first sheet accommodation section), a sliding cassette  5  (second sheet accommodation section), and a first restricting section  7  (restriction section). The main cassette  3  has a bottom member  30  (first bottom) on which a plurality of sheets are loaded. The bottom member  30  has a sheet loading surface F 1 . 
     The sliding cassette  5  has a bottom member  50  (second bottom) on which a plurality of sheets are loaded. The bottom member  50  has a sheet loading surface F 2 . The sliding cassette  5  is slidably attached to the main cassette  3 . More specifically, the sliding cassette  5  is attached to the main cassette  3  so as to be slidable between a retracted position where the sliding cassette  5  is retracted in the main cassette  3  and an extended position where the sliding cassette  5  is drawn out from the main cassette  3  in a direction A 1  away from the main cassette  3  (hereinafter, referred to as an “extending direction A 1 ”). In  FIG. 1 , the sliding cassette  5  is in the retracted position. The restricting section  7  restricts sliding of the sliding cassette  5  in the retracted position. 
       FIG. 2  is an enlarged perspective view of the first restricting section  7  of the sheet cassette  1 .  FIG. 3  is a cross-sectional view illustrating an engaged state of the first restricting section  7 , taken along line III-III in  FIG. 2  (first engaged position). In  FIG. 3 , the sliding cassette  5  is in the retracted position. Furthermore, in  FIG. 3 , no sheets are loaded in the sheet cassette  1 , and no external force is exerted on a projected portion  76 .  FIG. 4  is a cross-sectional view illustrating a disengaged state of the first restricting section  7  (disengaged position). 
     The first restricting section  7  includes an engagement pawl  38   a  (first engagement section), a lever section  70 , and a mating engagement pawl  78   a  (second engagement section). The engagement pawl  38   a  is disposed in the bottom member  30  of the main cassette  3 . The lever section  70  is disposed in the bottom member  50  of the sliding cassette  5 . The lever section  70  extends from the bottom member  50  in the extending direction A 1 . The mating engagement pawl  78   a  is disposed in the lever section  70  and is engageable with the engagement pawl  38   a . The engagement between the engagement pawl  38   a  and the mating engagement pawl  78   a  can be released by lifting the lever section  70 . 
     The lever section  70  includes a proximal end portion  72 , a lower portion  75 , and the projected portion  76  (distal end portion). The proximal end portion  72  is connected with the bottom member  50 . The lever section  70  starts from the proximal end portion  72  and extends in the extending direction A 1 . The lower portion  75  is formed continuous from the proximal end portion  72  and disposed lower than the sheet loading surface F 2  of the bottom member  50 . The projected portion  76  is the distal end portion of the lever section  70  in the extending direction A 1 . The projected portion  76  is formed continuous from the lower portion  75  and projected upward from the sheet loading surface F 2 . The proximal end portion  72  is elastic, and thus the projected portion  76  is swingable in upward and downward directions (in an upward direction B 1  or in a downward direction B 2 ). 
     The lever section  70  is shiftable from the first engaged position ( FIG. 3 ) to the disengaged position ( FIG. 4 ) when so manipulated. A second engaged position will be described later. As illustrated in  FIG. 3 , the first engaged position is a position where while the sliding cassette  5  is in the retracted position, no sheets are loaded on the bottom member  50 , the projected portion  76  protrudes from the sheet loading surface F 2  of the bottom member  50 , and the engagement pawl  38   a  and the mating engagement pawl  78   a  are in engagement. Posture of the lever section  70  while in the first engaged position may be referred to as a first posture. As illustrated in  FIG. 4 , the disengaged position is a position where while the sliding cassette  5  is in the retracted position, the lever section  70  is lifted out of the first engaged position, and thus the engagement between the engagement pawl  38   a  and the mating engagement pawl  78   a  is released. Posture of the lever section  70  while in the disengaged position may be referred to as a third posture. 
     Shift of the lever section  70  from the first engaged position to the disengaged position releases the engagement between the engagement pawl  38   a  and the mating engagement pawl  78   a , and allows the lever section  70  to be pulled in the extending direction A 1  to slide the sliding cassette  5  and extend a size of the sheet cassette  1 . As a result, the sliding cassette  5  is slid from the retracted position to the extended position. 
     That is, when the sliding cassette  5  is in the retracted position, it is possible to slide out the sliding cassette  5  up to the extended position by pulling the lever portion  70  in the extending direction A 1  while the engagement between the engagement pawl  38   a  and the mating engagement pawl  78   a  is kept released by lifting the lever section  70 , that is, while the lever section  70  is in the disengaged position. 
       FIG. 5  is a cross-sectional view illustrating a second restricting section  21  of the sheet cassette  1 , taken along line V-V going through an engagement hole  41  illustrated in  FIG. 1 . In  FIG. 5 , the sliding cassette  5  is in the extended position. As illustrated in  FIGS. 1 and 5 , the sheet cassette  1  further includes the second restricting section  21 . The second restricting section  21  restricts sliding of the sliding cassette  5  in the extended position. 
     The second restricting section  21  includes a pair of engagement holes  41  and a pair of engagement protrusions  61 . The engagement holes  41  are through holes formed in the bottom member  50  of the sliding cassette  5 . In the first embodiment, the engagement holes  41  are each rectangular and are formed in a region of the bottom member  50  that is closest to a forward end member  32 . 
     The engagement protrusions  61  are formed in the bottom member  30  of the main cassette  3  so that the engagement protrusions  61  mate with the engagement holes  41  when the sliding cassette  5  is in the extended position. In the first embodiment, the engagement protrusions  61  are each formed in a region of the bottom member  30  that is closer to a rearward end member  52 . The engagement protrusions  61  have a triangular cross-section and project from the sheet loading surface F 1 . The engagement protrusions  61  each have an engagement surface  62  and an inclined surface  63 . The inclined surface  63  is inclined upward in a contracting direction A 2  from the sheet loading surface F 1 . The contracting direction A 2 , which is opposite to the extending direction A 1 , is a direction in which the sliding cassette  5  moves toward the main cassette  3 . 
     As the sliding cassette  5  is drawn out in the extending direction A 1  into the extended position, each of the engagement protrusions  61  comes in engagement with the corresponding engagement hole  41 . Specifically, the engagement surface  62  of the engagement protrusion  61  comes in engagement with an engagement surface  42  forming the engagement hole  41 . As a result, sliding of the sliding cassette  5  in the extended position is restricted. 
     However, since the inclined surface  63  is inclined upward in the contracting direction A 2 , merely pushing in the sliding cassette  5  in the contracting direction A 2  can release the engagement (mating) between the engagement protrusions  61  and the engagement holes  41 , and bring the sliding cassette  5  into the retracted position. Therefore, no special engagement (mating) releasing mechanism is needed in order to shift the sliding cassette  5  from the extended position to the retracted position. 
     As described with reference to  FIG. 4 , a user shifts the lever section  70  from the first engaged position to the disengaged position to release the engagement, and subsequently pulls the lever section  70  in the extending direction A 1  or pushes the lever section  70  in the contracting direction A 2  to slide in or out the sliding cassette  5 . That is, the releasing of the engagement and the sliding can be performed by a series of manipulation actions on the lever section  70 . Consequently, the size of the sheet cassette  1  can be adjusted by simple manipulation. 
       FIG. 6  illustrates the engaged state of the first restricting section  7 , during which the lever section  70  is in the second engaged position. In  FIG. 6 , a plurality of sheets P are loaded in the sheet cassette  1 . The second engaged position is a position where while the sliding cassette  5  is in the retracted position, the projected portion  76  is pushed down out of the first engaged position in accordance with the number of sheets P loaded on the bottom member  50 , and the engagement pawl  38   a  and the mating engagement pawl  78   a  are in engagement. Posture of the lever section  70  in the second engaged position may be referred to as a second posture. Strength of the engagement between the engagement pawl  38   a  and the mating engagement pawl  78   a  is larger when the lever section  70  is in the second engaged position than when the lever section  70  is in the first engaged position.  FIG. 6  illustrates a situation in which the projected portion  76  is retracted below the sheet loading surface F 2  and the engagement strength is at its maximum. 
     Since the lever section  70  is shifted from the first engaged position to the second engaged position by the projected portion  76  pushed down due to loading of the sheets P, the strength of the engagement between the engagement pawl  38   a  and the mating engagement pawl  78   a  is increased. As a result, the locked state of the main cassette  3  and the sliding cassette  5  can be prevented from being released after loading of the sheets P. 
     As described with reference to  FIGS. 3, 4, and 6 , the lever section  70  is shiftable between the first engaged position ( FIG. 3 ), the second engaged position ( FIG. 6 ), and the disengaged position ( FIG. 4 ) while the sliding cassette  5  is in the retracted position. 
     [General Configuration of Sheet Cassette  1 ] 
     General configuration of the sheet cassette  1  will be described with reference to  FIG. 1 . In the first embodiment, an X axis and a Y axis are horizontal axes perpendicular to one another, and a Z axis is a vertical axis. The extending direction A 1  and the contracting direction A 2  are substantially parallel to the X axis. A sheet conveyance direction in the sheet cassette  1  is substantially the same as the contracting direction A 2 , and a direction opposite to the sheet conveyance direction is substantially the same as the extending direction A 1 . In embodiments of the present invention, a “forward end” or a “forward end portion” of a member or section refers to a forward end or a forward end portion of the member or section in the contracting direction A 2 , that is, a forward end or a forward end portion of the member or section in the sheet conveyance direction. A “rearward end” or a “rearward end portion” of a member or section refers to a rearward end or a rearward end portion of the member or section in the contracting direction A 2 , that is, a rearward end or a rearward end portion of the member or section in the sheet conveyance direction. A positive direction of the Z axis is the upward direction B 1 , and a negative direction of the Z axis is the downward direction B 2  (see  FIG. 3 ).  FIG. 1  illustrates the sheet cassette  1  in a minimum size state with the sliding cassette  5  pushed in the contracting direction A 2  to the maximum. 
     The sliding cassette  5  is slidable in the extending direction A 1  relative to the main cassette  3 . Sliding the sliding cassette  5  in the extending direction A 1  therefore extends the size of the sheet cassette  1 , allowing larger-sized sheets P to be loaded in the sheet cassette  1 . The sliding cassette  5  is slidable also in the contracting direction A 2  relative to the main cassette  3 . Sliding the sliding cassette  5  in the contracting direction A 2  therefore contracts the size of the sheet cassette  1 , allowing smaller-sized sheets P to be loaded in the sheet cassette  1 . In the first embodiment, the sheet cassette  1  can be adjusted to a normal size with the sliding cassette  5  pushed in to the maximum and to an extended size with the sliding cassette  5  drawn out to the maximum. The extended size defines a maximum size of sheets P that can be loaded in the sheet cassette  1 . 
     The main cassette  3  is formed mainly from a synthetic resin. Examples of the synthetic resin include acrylonitrile butadiene styrene (ABS) resins. The main cassette  3  includes the plate-like bottom member  30 , a pair of side end members  31 , the forward end member  32 , a panel  33 , a lift plate  35 , a pair of shafts  36 , and a pair of side end guides  34 . The main cassette  3  is open at a rearward end thereof. The forward end member  32  is stood from the bottom member  30  and elongated along the Y axis. A sheet conveyance guide  8  and a retard roller  6   a  are disposed in the forward end member  32 . The panel  33  is disposed on a front surface of the forward end member  32 . The pair of side end members  31  are opposite to one another, stood from the bottom member  30 , and elongated along the X axis. 
     The pair of shafts  36  are disposed corresponding to the pair of side end members  31 . The lift plate  35  is disposed on the sheet loading surface F 1  of the bottom member  30 . Each side of a proximal end portion of the lift plate  35  has a supporting hole (not shown) through which the corresponding one of the shafts  36  penetrates. Each end of the proximal end portion of the lift plate  35  is rotatably supported by the shaft  36 . Thus, a distal end portion of the lift plate  35  can be lifted up and down, rotating about the shafts  36 . 
     The pair of side end guides  34  are disposed opposite to one another and corresponding to the pair of side end members  31 . Each side end guide  34  is stood along the corresponding one of the side end members  31 . The pair of side end guides  34  are connected with a rack-and-pinion mechanism (not shown). Accordingly, the pair of side end guides  34  are geared to one another and movable in directions toward one another or in directions away from one another along the Y axis. 
     The sliding cassette  5  is formed manly from a synthetic resin (for example, an ABS resin). The sliding cassette  5  includes the first restricting section  7 , the plate-like bottom member  50 , a pair of side end members  51 , a rearward end member  52 , a rearward end guide  53 , a pair of rails  54 , and a plurality of ratchet teeth  55 . The first restricting section  7  is disposed in the bottom member  50 . The sliding cassette  5  is open at a forward end thereof. The pair of side end members  31  are opposite to one another, stood from the bottom member  50 , and elongated along the X axis. The rearward end member  52  is stood from the bottom member  30  and elongated along the Y axis. 
     The pair of rails  54  are formed on the bottom member  50  and elongated along the X axis. The plurality of ratchet teeth  55  are disposed between the pair of rails  54 , along the X axis. The rearward end guide  53  is stood along the rearward end member  52 . The rearward end guide  53  is movable along the rails  54 . Engagement pawls  56  are formed in a lower part of the rearward end guide  53 . The engagement pawls  56  can engage with the ratchet teeth  55  and disengage from the ratchet teeth  55 . Thus, the rearward end guide  53  can be fixed at any location along the rails  54 . 
     The sliding cassette  5  is attached to the main cassette  3  such that the bottom member  50  is disposed over the bottom member  30  in a region where the sliding cassette  5  overlaps the main cassette  3 . The sheets P are stacked on one another in the positive direction of the Z axis over the sheet loading surface F 1  of the bottom member  30 , an upper surface of the lift plate  35 , and the sheet loading surface F 2  of the bottom member  50 . More specifically, a forward end portion of the sheets P is placed over the sheet loading surface F 1  and the upper surface of the lift plate  35 , whereas a rearward end portion of the sheets P is placed over the sheet loading surface F 2 . The pair of side end guides  34  and the rearward end guide  53  are moved according to the size of the sheets P to be placed. 
     [Structure of Lever Section  70 ] 
     Structural detail of the lever section  70  will be described with reference to  FIGS. 2 and 3 . In  FIGS. 2 and 3 , the lever section  70  is in the first engaged position. The lever section  70  is formed integrally with the bottom member  50 . The lever section  70  is plate-like. The lever section  70  is formed from an elastic material or formed to have elasticity. Thus, it is possible to easily form the lever section  70  that can be shifted upward and downward. 
     The lower portion  75  of the lever section  70  is located higher than the bottom member  30  and lower than the bottom member  50 , and is substantially parallel to the bottom member  50  and to the bottom member  30 . The projected portion  76  of the lever section  70  has a curved outer edge. The projected portion  76  is formed continuous from one end (more specifically, a rearward end) of the lower portion  75 . The projected portion  76  is inclined relative to the lower portion  75  and projected in a diagonal upward direction from the lower portion  75  toward the extending direction A 1 . The projected portion  76  protrudes from the sheet loading surface F 2  of the bottom member  50  by a distance d 1 . 
     The lever section  70  has a cylindrical through hole  74  to be caught by a finger of a user. The finger catches in the through hole  74  at a side thereof corresponding to the projected portion  76 . More specifically, the through hole  74  is formed in the lever section  70  so as to span across the lower portion  75  and the projected portion  76 . The through hole  74  penetrates through an upper surface and a lower surface of the lever section  70 . 
     The lever section  70  has a second opposed region  77  that is opposed to a first opposed region  37  according to a position of the lever section  70 . The lower surface of the lower portion  75  of the lever section  70  is the second opposed region  77 . The mating engagement pawl  78   a  is formed in the second opposed region  77 . It should be noted that the main cassette  3  has the first opposed region  37  that is opposed to the lever section  70  according to the position of the lever section  70 . The engagement pawl  38   a  is formed in the first opposed region  37 . 
     One end (more specifically, a rearward end) of the proximal end portion  72  is connected with the other end (more specifically, the forward end) of the lower portion  75 . The other end (more specifically, a forward end) of the proximal end portion  72  is connected with the bottom member  50 . The proximal end portion  72  is inclined downward from the bottom member  50  toward the lower portion  75 . The lower portion  75  is therefore disposed at a position lower than the sheet loading surface F 2  of the bottom member  50  by a distance d 2 . 
     [Shift of Lever Section  70 ] 
     Shift of the lever section  70  will be described with reference to  FIGS. 3 and 4 . As illustrated in  FIG. 3 , the lever section  70  is in the first engaged position while no sheets P are loaded in the sheet cassette  1  and no external force is exerted on the projected portion  76 . As illustrated in  FIG. 4 , the lever section  70  is shifted from the first engaged position to the disengaged position when external force in the upward direction B 1  is exerted on the projected portion  76  and thus the projected portion  76  is pulled up. That is, the lever section  70  is shifted to the disengaged position when no sheets P are loaded in the sheet cassette  1  and external force in the upward direction B 1  is exerted on the projected portion  76 . 
     More specifically, the projected portion  76  is a free end portion. Therefore, the external force shifts the lever section  70  in the upward direction B 1  about the proximal end portion  72  from the first engaged position to the disengaged position. When the external force is released while the lever section  70  is in the disengaged position, the projected portion  76  is lowered due to the elasticity of the proximal end portion  72  such that the lever section  70  is shifted back to the first engaged position. 
     The user can put a finger in the through hole  74 , catch the projected portion  76  with the finger, and pull up the projected portion  76  in the upward direction B 1 . As a result, the user can shift the lever section  70  into the disengaged position. The user can then release the finger from the lever section  70  or relax the force thereby to let the projected portion  76  move in the downward direction B 2  so that the lever section  70  is shifted from the disengaged position back to the first engaged position. 
     [Structure of Engagement Pawl  38   a  and Mating Engagement Pawl  78   a]   
     Structure of the engagement pawl  38   a  and the mating engagement pawl  78   a  will be described with reference to  FIG. 3 . The engagement pawl  38   a  projects from the bottom member  30  of the main cassette  3 . More specifically, the engagement pawl  38   a  projects from the first opposed region  37 . The engagement pawl  38   a  has an engagement surface  38   c  and an inclined surface  38   d . The inclined surface  38   d  is on an opposite side of the engagement pawl  38   a  to the engagement surface  38   c . The inclined surface  38   d  is inclined upward in the contracting direction A 2  from the first opposed region  37 . 
     The mating engagement pawl  78   a  projects from the lever section  70  of the sliding cassette  5 . More specifically, the mating engagement pawl  78   a  projects from the second opposed region  77 . The mating engagement pawl  78   a  has an engagement surface  78   c  and an inclined surface  78   d . The inclined surface  78   d  is on an opposite side of the mating engagement pawl  78   a  to the engagement surface  78   c . The inclined surface  78   d  is inclined downward in the extending direction A 1  from the second opposed region  77 . 
     [Restriction of Sliding of Sliding Cassette  5 ] 
     Restriction of the sliding of the sliding cassette  5  will be described with reference to  FIGS. 3 and 6 . First, restriction of the sliding when the lever section  70  is in the first engaged position will be described. While the lever section  70  is in the first engaged position at an engagement point, the engagement pawl  38   a  and the mating engagement pawl  78   a  are in engagement. The engagement point is where the engagement pawl  38   a  is opposite to the mating engagement pawl  78   a . More specifically, the engagement surface  38   c  and the engagement surface  78   c  are in engagement. Accordingly, the sliding of the sliding cassette  5  in the extending direction A 1  is restricted. The position of the sliding cassette  5  with the engagement pawl  38   a  and the mating engagement pawl  78   a  in engagement is a position where the sliding cassette  5  is pushed in the contracting direction A 2  to the maximum, that is, the retracted position. Accordingly, the sliding cassette  5  is locked in a position where the size of the sheet cassette  1  is a minimum size. 
     Next, restriction of the sliding in a situation in which the sheets P are loaded in the sheet cassette  1  will be described. The lever section  70  is in the first engaged position before the sheets P are loaded in the sheet cassette  1 . Once the sheets P are loaded in the sheet cassette  1 , the projected portion  76  in contact with the sheets P receives the weight of the sheets P. The lever section  70  is therefore pushed down by the sheets P and shifted to the second engaged position. That is, the weight of the sheets P shifts the lever section  70  in the downward direction B 2  about the proximal end portion  72  to the second engaged position. The distance of the shift of the lever section  70  can increase up to the distance d 1  (see  FIG. 3 ) with increase in the weight of the sheets loaded. Strength of the engagement between the engagement pawl  38   a  and the mating engagement pawl  78   a  therefore increases with increase in the weight of the sheets loaded. The strength of the engagement is increased for the following reason. 
     Generally, sheets loaded in a sheet cassette move in a sheet cassette moving direction when the sheet cassette is inserted into an image forming apparatus. The moving sheets are received by a rearward end and a rearward end guide of the sliding cassette. Consequently, a load according to the weight of the sheets is placed on the rearward end and the rearward end guide. In particular, in a situation in which many sheets are loaded or sheets having a larger size are loaded, the load on the rearward end and the rearward end guide is larger. As a result, the sliding cassette may be unintendedly unlocked. 
     In the first embodiment, shift of the lever section  70  to the second engaged position allows the strength of the engagement between the engagement pawl  38   a  and the mating engagement pawl  78   a  to increase with increase in the weight of the sheets loaded, preventing unlocking of the sliding cassette  5  due to a load resulting from the movement of the sheets P. 
     Once the projected portion  76  of the lever section  70  is shifted in the downward direction B 2  by the distance d 1 , the sheets P become supported by the sheet loading surface F 2  of the sliding cassette  5 . Thus, the projected portion  76  is prevented from being further shifted in the downward direction B 2  by more than the distance d 1 . As a result, deformation or damage that prevents the lever section  70  from returning to the first engaged position can be restricted. 
     [Removal of Restriction of Sliding of Sliding Cassette  5 ] 
     Removal of restriction of the sliding of the sliding cassette  5  will be described with reference to  FIGS. 3 and 4 . When external force in the upward direction B 1  is exerted on the projected portion  76  of the lever section  70 , and thus the lever section  70  is shifted from the position with the engagement pawl  38   a  and the mating engagement pawl  78   a  in engagement to the disengaged position, the mating engagement pawl  78   a  disengages from the engagement pawl  38   a  thereby to release the engagement therebetween. Thus, the restriction of the sliding of the sliding cassette  5  is removed. That is, the sliding cassette  5  is unlocked. When external force in the extending direction A 1  is exerted on the lever section  70 , the sliding cassette  5  slides in the extending direction A 1 . The sliding cassette  5  is drawn in the extending direction A 1  to the maximum and locked by the second restricting section  21  in a position where the size of the sheet cassette  1  is a maximum size, that is, in the extended position. 
     A user for example extends the size of the sheet cassette  1  according to the following procedure. The user puts a finger in the through hole  74 , catches the projected portion  76  of the lever section  70  with the finger, and pulls up the projected portion  76 . As a result, the lever section  70  is shifted to the disengaged position, the engagement is released, and the restriction of the sliding is removed. Subsequently to the removal of the restriction of the sliding, the user catches a rear-side opening edge of the through hole  74  with a finger and pulls the finger in the extending direction A 1 . Consequently, the sliding cassette  5  can be drawn, and the size of the sheet cassette  1  can be extended. The sliding cassette  5  is drawn out by a prescribed distance, and stopped and locked by the second restricting section  21 . 
     A user for example contracts the size of the sheet cassette  1  according to the following procedure. The user pushes in the sliding cassette  5  in the contracting direction A 2  until the mating engagement pawl  78   a  comes in engagement with the engagement pawl  38   a . Since the engagement pawl  38   a  has the inclined surface  38   d  and the mating engagement pawl  78   a  has the inclined surface  78   d , the mating engagement pawl  78   a  can smoothly engage with the engagement pawl  38   a  as a result of the sliding of the sliding cassette  5  in the contracting direction A 2 . 
     [Structure of Cutout Portion  39 ] 
     A structure of the cutout portion  39  will be described with reference to  FIGS. 2 and 3 . The bottom member  30  of the main cassette  3  has the cutout portion  39 . More specifically, the cutout portion  39  extends in the extending direction A 1  from a specified location in the bottom member  30  to a rearward end of the bottom member  30 . The cutout portion  39  is formed by cutting out a U-shaped portion from a rearward end portion of the bottom member  30 . The cutout portion  39  is formed corresponding to a region of movement of the through hole  74  in accompaniment to the sliding of the sliding cassette  5 . Accordingly, the through hole  74  moves above the cutout portion  39  in accompaniment to the sliding of the sliding cassette  5  in the extending direction A 1  or in the contracting direction A 2 . As a result, the user can avoid contact of their finger with the bottom member  30  of the main cassette  3  and slide the sliding cassette  5  without pulling the finger out of the through hole  74 . In the first embodiment, the cutout portion  39  is formed by cutting out a U-shaped portion from the rearward end portion of the bottom member  30 . 
     According to the first embodiment, it is possible to adjust the size of the sheet cassette  1  by simple manipulation and restrict release of the locked state of the main cassette  3  and the sliding cassette  5  after loading of the sheets P as described above with reference to  FIGS. 1 to 6 . 
     Furthermore, according to the first embodiment, the engagement pawl  38   a  can be formed integrally with the main cassette  3 , and the lever section  70  and the mating engagement pawl  78   a  can be formed integrally with the sliding cassette  5  as described with reference to  FIGS. 2 and 3 . It is therefore possible to form a mechanism for unlocking the sliding cassette  5  with a reduced number of elements. 
     Furthermore, according to the first embodiment, the engagement pawl  38   a  and the mating engagement pawl  78   a  allow the locking and the unlocking of the sliding cassette  5  to be readily performed as described with reference to  FIGS. 3 and 4 . 
     Furthermore, according to the first embodiment, the lever section  70  has the through hole  74  as described with reference to  FIG. 2 . Accordingly, a user can readily unlock the sliding cassette  5  by putting a finger in the through hole  74  and pulling up the lever section  70 . 
     Second Embodiment 
     The sheet cassette  1  according to the second embodiment of the present invention will be described with reference to  FIGS. 1, 2, and 7 to 9 . Configuration of the sheet cassette  1  according to the second embodiment is the same as the configuration of the sheet cassette  1  according to the first embodiment except a part of the first restricting section  7 . Therefore, the sheet cassette  1  illustrated in  FIGS. 1 and 2  will be described as the sheet cassette  1  according to the second embodiment. Hereinafter, a difference between the second embodiment and the first embodiment will be mainly described. 
       FIG. 7  is a cross-sectional view taken along line VII-VII in  FIG. 2 , illustrating the engaged state of the first restricting section  7  in the sheet cassette  1  adjusted to a small size. In  FIG. 7 , the sliding cassette  5  is in the retracted position, and the lever section  70  is in the first engaged position. The first restricting section  7  (restricting section) includes a plurality of engagement holes  38   b  (a plurality of first engagement sections), the lever section  70 , and an engagement protrusion  78   b  (second engagement section). In the second embodiment, the plurality of engagement holes  38   b  are provided instead of the engagement pawl  38   a  (see  FIG. 3 ) of the first embodiment, and the engagement protrusion  78   b  is provided instead of the mating engagement pawl  78   a  (see  FIG. 3 ) of the first embodiment. 
     The engagement holes  38   b  function as locking portions. The plurality of engagement holes  38   b  are three engagement holes  38   b  in the second embodiment. Of the three engagement holes  38   b , an engagement hole  38   b  closest to the rearward end of the bottom member  30  may be referred to as an engagement hole  38   b   1 , an engagement hole  38   b  adjacent to the engagement hole  38   b   1  may be referred to as an engagement hole  38   b   2 , and an engagement hole  38   b  farthest from the rearward end of the bottom member  30  may be referred to as an engagement hole  38   b   3 . The configuration of the lever section  70  is the same as the configuration of the lever section  70  of the first embodiment (see  FIG. 3 ). 
     In the second embodiment, the first engaged position is a position where while the sliding cassette  5  is in the retracted position, no sheets are loaded on the bottom member  50 , the projected portion  76  protrudes from the sheet loading surface F 2  of the bottom member  50 , and the engagement protrusion  78   b  is in engagement with one of the engagement holes  38   b . The second engaged position is a position where while the sliding cassette  5  is in the retracted position, the projected portion  76  is pushed down out of the first engaged position in accordance with the number of sheets loaded on the bottom member  50 , and the engagement hole  38   b  and the engagement protrusion  78   b  are in engagement. The disengaged position is a position where while the sliding cassette  5  is in the retracted position, the lever section  70  is lifted out of the first engaged position, and thus the engagement between the engagement hole  38   b  and the engagement protrusion  78   b  is released. 
     The plurality of engagement holes  38   b  are formed in the bottom member  30  of the main cassette  3 . More specifically, the plurality of engagement holes  38   b  are formed in the first opposed region  37 . In the second embodiment, each of the plurality of engagement holes  38   b  is a cylindrical through hole. Alternatively, each of the plurality of engagement holes  38   b  may be a bottomed recess. The plurality of engagement holes  38   b  are arranged along the extending direction A 1 . 
     Locations of the engagement holes  38   b  are determined according to a maximum size of sheets P that can be loaded in the sheet cassette  1  while the engagement protrusion  78   b  and one of the engagement holes  38   b  are in engagement. The engagement protrusion  78   b  protrudes from the lever section  70  of the sliding cassette  5 . More specifically, the engagement protrusion  78   b  protrudes from the second opposed region  77 . The engagement protrusion  78   b  has a cylindrical shape that can mate with each of the engagement holes  38   b . The engagement holes  38   b  therefore have a slightly larger diameter than a diameter of the engagement protrusion  78   b.    
     First, restriction of sliding by engagement (mating) between the engagement holes  38   b  and the engagement protrusion  78   b  when the lever section  70  is in the first engaged position will be described. While the lever section  70  is in the first engaged position at an engagement point, the engagement protrusion  78   b  is in engagement with one of the engagement holes  38   b . The engagement point is where the one of the engagement holes  38   b  is opposite to the engagement protrusion  78   b . More specifically, the engagement protrusion  78   b  is mating with one of the engagement holes  38   b . Accordingly, the sliding of the sliding cassette  5  in the extending direction A 1  and in the contracting direction A 2  is restricted, and the sliding cassette  5  is locked. In the second embodiment, the term engagement and the term mating have the same meaning. 
     Next, restriction of the sliding in a situation in which the sheets P are loaded in the sheet cassette  1  will be described.  FIG. 8  illustrates a cross-section of the first restricting section  7  when the lever section  70  is in the second engaged position. In  FIG. 8 , a plurality of sheets P are loaded in the sheet cassette  1 , and the sliding cassette  5  is in the retracted position. 
     As in the first embodiment, the projected portion  76  is pushed down by the weight of the sheets P, and the lever section  70  is shifted in the downward direction B 2  about the proximal end portion  72  to the second engaged position. Strength of the engagement between the engagement hole  38   b  and the engagement protrusion  78   b  is larger when the lever section  70  is in the second engaged position than when the lever section  70  is in the first engaged position.  FIG. 8  illustrates a situation in which the projected portion  76  is retracted below the sheet loading surface F 2  and the engagement strength is at its maximum. 
     More specifically, the distance of the shift of the lever section  70  can increase up to the distance d 1  (see  FIG. 7 ) with increase in the weight of the sheets loaded. Thus, the engagement protrusion  78   b  mates with the engagement hole  38   b  more deeply when the lever section  70  is in the second engaged position than when the lever section  70  is in the first engaged position, and strength of the engagement between the engagement hole  38   b  and the engagement protrusion  78   b  increases with increase in the weight of the sheets loaded. As a result, as in the first embodiment, unlocking of the sliding cassette  5  due to a load resulting from the movement of the sheets P can be prevented. Since the projected portion  76  is not shifted downward by more than the distance d 1  as in the first embodiment, deformation or damage that prevents the lever section  70  from returning to the first engaged position can be restricted. 
     Next, adjustment of the size of the sheet cassette  1  will be described. Since there are three engagement holes  38   b   1  to  38   b   3  in the second embodiment, the sheet cassette  1  is adjustable to three different sizes. The three different sizes are a large size, a medium size, and a small size. The sliding cassette  5  is in the retracted position when the sheet cassette  1  is in the small size, in the first extended position when in the medium size, and in the second extended position when in the large size. 
     The small size of the sheet cassette  1  will be described with reference to  FIGS. 7 and 8 . The engagement protrusion  78   b  is caused to mate with the engagement hole  38   b   3  by positioning the lever section  70  in the first engaged position or in the second engaged position. Accordingly, the sliding cassette  5  is in a position where the sliding cassette  5  is pushed in the contracting direction A 2  to the maximum. As a result, the sliding cassette  5  is locked in a position where the sheet cassette  1  is in the small size. 
     Although not shown, the sliding cassette  5  is locked in a position where the sheet cassette  1  is in the medium size when the engagement protrusion  78   b  is mating with the engagement hole  38   b   2  and the sliding cassette  5  is locked in a position where the sheet cassette  1  is in the large size when the engagement protrusion  78   b  is mating with the engagement hole  38   b   1 , with the lever section  70  in the first engaged position or in the second engaged position. 
     The second restricting section  21  (see  FIGS. 1 and 5 ) in the second embodiment has a pair of engagement holes  41  and a pair of engagement protrusions  61  formed according to the position of the engagement hole  38   b   2 , and another pair of engagement holes  41  and another pair of engagement protrusions  61  formed according to the position of the engagement hole  38   b   1 . Accordingly, when the engagement protrusion  78   b  is mating with the engagement hole  38   b   2 , the pair of engagement holes  41  and the pair of engagement protrusions  61  formed according to the position of the engagement hole  28   b   2  are mating with one another to lock the sliding cassette  5  in the position where the sheet cassette  1  is in the medium size. When the engagement protrusion  78   b  is mating with the engagement hole  38   b   1 , the pair of engagement holes  41  and the pair of engagement protrusions  61  formed according to the position of the engagement hole  38   b   1  are mating with one another to lock the sliding cassette  5  in the position where the sheet cassette  1  is in the large size. 
     Next, removal of the restriction of the sliding by releasing the engagement (releasing the mating) between one of the engagement holes  38   b  and the engagement protrusion  78   b  will be described.  FIG. 9  is a cross-sectional view illustrating the disengaged state. In  FIG. 9 , the lever section  70  is in the disengaged position. Once external force in the upward direction B 1  is exerted on the projected portion  76  of the lever section  70  in the first engaged position with the engagement protrusion  78   b  mating with one engagement hole  38   b , the lever section  70  is shifted to the disengaged position, and thus the engagement protrusion  78   b  is pulled out of the engagement hole  38   b , releasing the mating therebetween. Thus, the restriction of the sliding of the sliding cassette  5  is removed. That is, the sliding cassette  5  is unlocked. 
     When external force in the extending direction A 1  is subsequently exerted on the lever section  70 , the sliding cassette  5  slides in the extending direction A 1 . Once the lever section  70  is shifted to the first engaged position after the sliding cassette  5  has been drawn in the extending direction A 1 , the engagement protrusion  78   b  mates with another engagement hole  38   b . As a result, the sliding is once again restricted, and the sliding cassette  5  is locked. 
     When external force in the contracting direction A 2  is exerted on the lever section  70  after release of the mating, the sliding cassette  5  slides in the contracting direction A 2 . Once the lever section  70  is shifted to the first engaged position after the sliding cassette  5  has been pushed in the contracting direction A 2 , the engagement protrusion  78   b  mates with yet another engagement hole  38   b . As a result, the sliding is once again restricted, and the sliding cassette  5  is locked. 
     A user for example extends or contracts the size of the sheet cassette  1  according to the following procedure. The user puts a finger in the through hole  74 , catches the projected portion  76  of the lever section  70  with the finger, and pulls up the projected portion  76 . As a result, the lever section  70  is shifted to the disengaged position, the mating between the engagement protrusion  78   b  and one engagement hole  38   b  is released, and the restriction of the sliding is removed. Subsequently to the removal of the restriction of the sliding, the user catches the rear-side opening edge of the through hole  74  with a finger and pulls the finger in the extending direction A 1  or pushes the projected portion  76  of the lever section  70  in the contracting direction A 2 . As a result, the sliding cassette  5  is drawn out or pushed in. The user subsequently causes the engagement protrusion  78   b  to mate with another engagement hole  38   b , thereby locking the sliding cassette  5  and extending or contracting the size of the sheet cassette  1 . 
     According to the second embodiment, it is possible to adjust the size of the sheet cassette  1  by simple manipulation and restrict release of the locked state of the main cassette  3  and the sliding cassette  5  after loading of the sheets P as described above with reference to  FIGS. 1, 2, and 7 to 9 . The second embodiment further produces the following effect in addition to the same effect as produced by the first embodiment. 
     That is, according to the second embodiment, the engagement holes  38   b  are formed by processing the main cassette  3 , and the lever section  70  and the engagement protrusion  78   b  can be formed integrally with the sliding cassette  5  as described with reference to  FIG. 7 . It is therefore possible to form a mechanism for unlocking the sliding cassette  5  with a reduced number of elements. 
     Furthermore, the second embodiment includes a plurality of engagement holes  38   b . The plurality of engagement holes  38   b  are arranged along the extending direction A 1 . Thus, the sheet cassette  1  is adjustable to a plurality of different sizes. 
     Furthermore, according to the second embodiment, the engagement protrusion  78   b  and the engagement holes  38   b  allow the locking and the unlocking of the sliding cassette  5  to be readily performed. 
     Third Embodiment 
     The sheet cassette  1  according to the third embodiment of the present invention will be described with reference to  FIGS. 1, 2, and 10 . Configuration of the sheet cassette  1  according to the third embodiment is the same as the configuration of the sheet cassette  1  according to the first embodiment except a part of the first restricting section  7 . Therefore, the sheet cassette  1  illustrated in  FIGS. 1 and 2  will be described as the sheet cassette  1  according to the third embodiment. Hereinafter, a difference between the third embodiment and the first embodiment will be mainly described. 
       FIG. 10A  is a cross-sectional view illustrating the engaged state of the first restricting section  7  (restricting section).  FIG. 10A  illustrates the lever section  70  in the first engaged position. 
     In the third embodiment, a plurality of engagement pawls  38   e  (a plurality of first engagement sections) are provided instead of the engagement pawl  38   a  (see  FIG. 3 ) of the first embodiment. Furthermore, the main cassette  3  includes a rack  73 . The rack  73  is disposed in the bottom member  30  of the main cassette  3  and is movable relative to the main cassette  3  in a sliding direction of the sliding cassette  5 . The sliding direction is the extending direction A 1  or the contracting direction A 2 . The rack  73  has the plurality of engagement pawls  38   e  arranged in the sliding direction of the sliding cassette  5 . As described above, an engagement structure that is engageable with the mating engagement pawl  78   a  is formed from the rack  73  having the plurality of engagement pawls  38   e  arranged in the sliding direction. The rack  73  has the first opposed region  37  that is opposed to the lever section  70  according to the position of the lever section  70 . The engagement pawls  38   e  are formed in the first opposed region  37 . 
       FIG. 10B  is a schematic view illustrating the rack  73 . Each engagement pawl  38   e  has a different length from a peak thereof to a peak of the mating engagement pawl  78   a  (hereinafter, referred to as an “engagement length”) when the lever section  70  is in the first engaged position. In the third embodiment, the plurality of engagement pawls  38   e  have protrusion amounts that increase stepwise in the extending direction A 1 . Detailed description thereof will be given below. 
     In the third embodiment, engagement pawls  38   e   1  to  38   e   3  are provided as the plurality of engagement pawls  38   e . Of engagement lengths D 1  to D 3 , the engagement length D 1  of the engagement pawl  38   e   1  is the longest, the engagement length D 3  of the engagement pawl  38   e   3  is the shortest, and the engagement length D 2  of the engagement pawl  38   e   2  is between the engagement length D 1  and the engagement length D 3 . 
     The longer the engagement length of an engagement pawl  38   e  is, the stronger the engagement between the engagement pawl  38   e  and the mating engagement pawl  78   a  is, and the tighter the locking of the sliding cassette  5  is. By contrast, the shorter the engagement length of an engagement pawl  38   e  is, the looser the locking of the sliding cassette  5  is, but the more operable the sliding cassette  5  is. That is, the easier unlocking and sliding the sliding cassette  5  is. 
     The rack  73  is secured to the bottom member  30  with an engagement surface  38   c  of one of the engagement pawls  38   e   1  to  38   e   3  at an engagement location E. In the third embodiment, therefore, a user can adjust the tightness of the locking of the sliding cassette  5  and the operability of the sliding cassette  5  to different degrees according to usage conditions by moving the rack  73 . 
     In a situation in which the sheet cassette  1  is used frequently by being filled with sheets P having a maximum size, for example, the user adjusts the position of the rack  73  so that the locking is tight. For example, the rack  73  is fixed so that the engagement pawl  38   e   1  is at the engagement location E. On the other hand, in a situation in which the sheet cassette  1  is used less frequently by being filled with sheets P having a maximum size, for example, the user adjusts the position of the rack  73  so that the locking is loose, giving priority to the operability. For example, the rack  73  is fixed so that the engagement pawl  38   e   3  is at the engagement location E. 
     Since the third embodiment has the same lever section  70  as the first embodiment, it is possible to adjust the size of the sheet cassette  1  by simple manipulation and restrict release of the locked state of the main cassette  3  and the sliding cassette  5  after loading of the sheets P. 
     In the third embodiment, the first engaged position is a position where while the sliding cassette  5  is in the retracted position, no sheets are loaded on the bottom member  50 , the projected portion  76  protrudes from the sheet loading surface F 2  of the bottom member  50 , and one engagement pawl  38   e  and the mating engagement pawl  78   a  are in engagement. The second engaged position is a position where while the sliding cassette  5  is in the retracted position, the projected portion  76  is pushed down out of the first engaged position in accordance with the number of sheets loaded on the bottom member  50 , and the engagement pawl  38   e  and the mating engagement pawl  78   a  are in engagement. The disengaged position is a position where while the sliding cassette  5  is in the retracted position, the lever section  70  is lifted out of the first engaged position, and thus the engagement between the engagement pawl  38   e  and the mating engagement pawl  78   a  is released. 
     Fourth Embodiment 
     An image forming apparatus  100  in the fourth embodiment of the present invention will be described with reference to  FIG. 11 .  FIG. 11  is a schematic cross-sectional view for illustrating an overview of the image forming apparatus  100 . The image forming apparatus  100  is for example a copier, a printer, or a multifunction peripheral. A multifunction peripheral for example has at least two of a copier, a printer, and a facsimile machine. Hereinafter, an example in which the image forming apparatus  100  is a printer will be described. 
     The image forming apparatus  100  includes a feeder  10 , an image forming section  80 , and a discharge section  90 . The image forming apparatus  100  also has a conveyance path L. The conveyance path L includes conveyance paths L 1  to L 3  and a conveyance path Lb. 
     The feeder  10  includes the sheet cassette  1 , a feeding section  2 , and a manual feed tray  9 . The sheet cassette  1  is the sheet cassette  1  according to the first embodiment (see  FIG. 3 ), the sheet cassette  1  according to the second embodiment (see  FIG. 7 ), or the sheet cassette  1  according to the third embodiment (see  FIG. 10 ). The sheet cassette  1  is disposed in a lower part of the image forming apparatus  100 . The sheet cassette  1  is drawable from a front surface of the image forming apparatus  100  in a negative direction of the X axis along the X axis. The panel  33  of the sheet cassette  1  forms a portion of the front surface of the image forming apparatus  100 . 
     The feeding section  2  feeds the sheets P loaded in the sheet cassette  1 . More specifically, the feeding section  2  includes a pickup roller  4  and a pair of feeding rollers  6 . The pair of feeding rollers  6  include a retard roller  6   a  and a feed roller  6   b . The pickup roller  4  feeds the sheets P loaded in the sheet cassette  1  to the pair of feeding rollers  6  while rotating. 
     The pair of feeding rollers  6  prevent multiple feeding of sheets P and feed the sheets P to the conveyance path L 1  one sheet at a time. More specifically, the feed roller  6   b  feeds the sheets P while rotating. When receiving one sheet P, the retard roller  6   a  is driven to rotate by the feed roller  6   b . When receiving a plurality of sheets P stuck on one another, on the contrary, the retard roller  6   a  rotates in a direction opposite to a direction for feeding the sheets P or stops to separate a sheet P in contact with the feed roller  6   b  from another sheet P. As a result, one sheet P is fed by the feed roller  6   b . The sheet P is conveyed to the image forming section  80  along the conveyance path L 1 . Sheets P are also loaded on the manual feed tray  9 . The sheets P are fed from the manual feed tray  9  to the conveyance path L 2  and further fed to the conveyance path L 1 . The sheets P are conveyed to the image forming section  80  along the conveyance path L 1 . 
     The image forming section  80  forms an image on a sheet P fed by the feeder  10 . More specifically, the image forming section  80  includes a photosensitive drum  81 , a charger  82 , a development section  83 , a transfer section  84 , a cleaning section  85 , a light exposure section  86 , a toner cartridge  87 , and a fixing section  88 . 
     The photosensitive drum  81  rotates in a direction along a conveyance direction C of the sheets P. The charger  82  charges a surface of the photosensitive drum  81 . The light exposure section  86  irradiates the surface of the photosensitive drum  81  with light based on image data. As a result, an electrostatic latent image based on the image data is formed on the surface of the photosensitive drum  81 . The development section  83  attaches toner to the electrostatic latent image to form a toner image on the surface of the photosensitive drum  81 . The toner cartridge  87  contains the toner and supplies the toner to the development section  83 . 
     The transfer section  84  presses the sheet P against the surface of the photosensitive drum  81  to transfer the toner image onto the sheet P. The sheet P having the toner image transferred thereon is conveyed to the fixing section  88  along the conveyance path L 2 . The fixing section  88  applies heat and pressure to the sheet P to fix the toner image on the sheet P. The sheet P on which the toner image has been fixed by the fixing section  88  is conveyed to the discharge section  90  along the conveyance path L 3 . The cleaning section  85  removes toner left on the surface of the photosensitive drum  81 . 
     The discharge section  90  includes a pair of discharge rollers  91  and an exit tray  92 . The pair of discharge rollers  91  discharge the sheet P conveyed thereto along the conveyance path L 3  to the exit tray  92 . When duplex printing is to be performed, the sheet P conveyed to the conveyance path L 3  is returned into the conveyance path L 1  along the conveyance path Lb. The sheet P is for example plain paper, recycled paper, thin paper, thick paper, or an overhead projector (OHP) sheet. 
     As described above, the image forming apparatus  100  according to the fourth embodiment includes the sheet cassette  1  according to the first embodiment, the sheet cassette  1  according to the second embodiment, or the sheet cassette  1  according to the third embodiment. It is therefore possible to adjust the size of the sheet cassette  1  by simple manipulation and restrict release of the locked state of the main cassette  3  and the sliding cassette  5  after loading of the sheets P. Other than that, the third embodiment produces the same effects as the first embodiment, the second embodiment, and the third embodiment. 
     The embodiments of the present invention have been described so far with reference to  FIGS. 1 to 11 . However, the present invention is not limited to the above-described embodiments and can be practiced in various ways within the scope without departing from the essence of the present invention. For example, the following alterations may be made. 
     (1) The first embodiment includes a single engagement pawl  38   a . Alternatively, a plurality of engagement pawls  38   a  may be formed. In this case, the plurality of engagement pawls  38   a  are arranged parallel to the extending direction A 1  as in the case of the plurality of engagement holes  38   b  according to the second embodiment. Thus, the sheet cassette  1  is adjustable to a plurality of different sizes. Furthermore, the second embodiment may have a single engagement hole  38   b.    
     (2) The engagement between the engagement pawl  38   a  and the mating engagement pawl  78   a  is released, the engagement between one engagement hole  38   b  and the engagement protrusion  78   b  is released, or the engagement between one engagement pawl  38   e  and the mating engagement pawl  78   a  is released by pulling up the lever section  70  in the upward direction B 1  in the first embodiment to the third embodiment. Alternatively, a configuration in which the engagement is released by pushing down the lever section  70  in the downward direction B 2  may be employed. 
     (3) A plurality of protrusions may be formed instead of the plurality of engagement holes  38   b , and an engagement hole may be formed instead of the engagement protrusion  78   b  in the second embodiment. 
     (4) The cutout portion  39  is formed in the bottom member  30  of the main cassette  3  in the first embodiment to the third embodiment. Alternatively, the main cassette  3  may have a through hole instead of the cutout portion  39 . More specifically, the through hole is formed in the bottom member  30  corresponding to the region of movement of the through hole  74  in accompaniment to the sliding of the sliding cassette  5 . A user can therefore slide the sliding cassette  5  without pulling their finger out of the through hole  74 . 
     (5) The projected portion  76  is projected in a diagonal upward direction from the lower portion  75  toward the extending direction A 1  in the first embodiment to the third embodiment. Alternatively, the projected portion  76  may be projected in a diagonal upward direction from the lower portion  75  toward the contracting direction A 2  or projected in a vertical upward direction from the lower portion  75 . 
     (6) The rack  73  is movable relative to the main cassette  3  in the sliding direction of the sliding cassette  5  in the third embodiment. Alternatively, the rack  73  may be fixed to the bottom member  30  so as to be non-movable relative to the main cassette  3 . Accordingly, the lever section  70  is disposed in the sliding cassette  5  so as to be movable relative to the sliding cassette  5  in the sliding direction of the sliding cassette  5 . As a result, it is possible to adjust the tightness of the locking of the sliding cassette  5  and the operability of the sliding cassette  5  to different degrees according to usage conditions as in the third embodiment. 
     (7) The lever section  70  is formed from an elastic material or formed so as to have elasticity in the first embodiment to the third embodiment. The lever section  70  may be formed as a separate member from the sliding cassette  5  and connected with the bottom member  50 . Examples of elastic materials include synthetic resins and metals. Examples of the lever section  70  formed so as to have elasticity include a plate spring. 
     (8) The sheet conveyance direction in the sheet cassette  1  is substantially the same as the contracting direction A 2  in the first embodiment to the fourth embodiment. Alternatively, the sheet conveyance direction may be different from the contracting direction A 2 . For example, the sheet conveyance direction may be substantially perpendicular to the contracting direction A 2 . 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to the fields of sheet cassettes in which a plurality of sheets are loaded, and of feeders and image forming apparatuses including the sheet cassettes.