Patent Publication Number: US-7708263-B2

Title: Image forming apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2005-138824, filed on May 11, 2005, the entire subject matter of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     Aspects of the present invention relate to an image forming apparatus that has a sheet member feed-in port on one side surface. 
     BACKGROUND 
     JP-A-2005-41652 discloses an apparatus in which a multipurpose tray  14  for hand insertion and a multipurpose feed mechanism unit  15  for feeding paper sheets on the multipurpose tray  14  and separating them one by one are disposed on a side surface of a laser printer  1 . The apparatus has a configuration wherein the paper sheets on the multipurpose tray  14  are fed and separated by one multipurpose feed roller  15   a  that is pressed against a multipurpose pad member  15   d.    
     SUMMARY 
     In the configuration disclosed in JP-A-2005-41652, the paper feed and the separation are performed by the multipurpose feed roller  15   a . Thus, the outer peripheral surface of this multipurpose feed roller  15   a  needs to abut on the paper sheets on the multipurpose tray  14  and needs to be pressed against the multipurpose pad member  15   d . Accordingly, the multipurpose feed roller  15   a  inevitably needs to have a large diameter. Moreover, the multipurpose feed roller  15   a  needs to be arranged on the side close to the multipurpose tray so that the roller  15   a  abuts on the paper sheets on the multipurpose tray  14 . Therefore the size of the whole laser printer  1  is enlarged in the horizontal direction and vertical direction. 
     Aspects of the invention provide an image forming apparatus that realizes reduction in the size of the image forming apparatus in, at least, the horizontal direction thereof while including a mechanism for feeding in a sheet member from a sheet member feed-in port. 
     According to an aspect of the invention, there is provided an image forming apparatus including: a housing that has a sheet member feed-in port, on a side of one side surface thereof, for feeding in a sheet member; a loading tray on which the sheet member to be fed into the sheet member feed-in port is loaded; a sheet member accommodation cassette that is arranged on a bottom side of the housing, a sheet member is accommodated in the sheet member accommodation cassette; a first conveyance passage formed within the housing, the sheet member accommodated in the sheet member accommodation cassette is conveyed in the first conveyance passage while being folded back from the side of the one side surface of the housing to an opposite side; a second conveyance passage extending from the sheet member feed-in port to a downstream end side of the first conveyance passage; a feed-in mechanism disposed in the second conveyance passage, the feed-in mechanism feeding the sheet member from the sheet member feed-in port to a side of a junction point between the first conveyance passage and the second conveyance passage; and a process unit that forms an image on the sheet member passed through the junction point, the process unit disposed on a downstream side in a conveyance direction of the sheet member with respect to the junction point; wherein the feed-in mechanism includes: a feed-in roller that feeds the sheet member loaded on the loading tray into the sheet member feed-in port; a separation member disposed on a downstream side in the conveyance direction of the sheet member with respect to the feed-in roller; and a separation roller that opposes to the separation member and delivers the sheet member to the side of the junction point; and wherein an opposition position between the separation member and the separation roller is located further from the one side surface than a part of the first conveyance passage and is located closer to the one side surface than the junction point. 
     Incidentally, the “image forming apparatus” is not limited to a printing apparatus such as printer (for example, laser printer), but it may well be a facsimile equipment or a multi function apparatus having a printer function, a scanner function, etc. 
     The “sheet member” includes a paper sheet, an OHP sheet, etc., as a recording member. 
     In the configuration, the feed-in mechanism which feeds in the sheet members on the loading tray and separates them one by one has been formed as a twin-roller type that includes the feed-in roller and the separation roller. Thus, each of the rollers can be made smaller in diameter than the multipurpose feed roller in the configuration of JP-A-2005-41652. Besides, the opposition position between the separation roller of small diameter and the separation member can be located on the further side of that U-shaped first conveyance passage which is nearest to one side surface of the housing, as viewed from the side of the side surface. On the other hand, on the side of the loading tray, the feed-in roller of small diameter abutting on the loaded paper sheets can be arranged. Accordingly, while the mechanism for feeding in the sheet members from the sheet member feed-in port is included, the size of the image forming apparatus in, at least, the horizontal direction thereof can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side sectional view of a laser printer according to an aspect of the present invention; 
         FIG. 2  is an enlarged side sectional view of the laser printer in the state where an MP tray is opened; 
         FIG. 3  is a perspective view of a partition member seen from the rear side thereof; 
         FIG. 4  is a perspective view showing a vertical movement drive mechanism of an MP feed roller (a state where the MP feed roller lies at the ascent position thereof); 
         FIG. 5  is a perspective view showing the vertical movement drive mechanism of the MP feed roller (a state where the MP feed roller lies at the descent position thereof); 
         FIG. 6  is a side view of the vertical movement drive mechanism in the state where the MP feed roller lies at its ascent position; 
         FIG. 7  is a side view of the vertical movement drive mechanism in the state where the MP feed roller lies at its descent position; 
         FIGS. 8A and 8B  are perspective views showing a sheet presence/absence sensor; 
         FIG. 9  is a perspective view of a roller unit and the MP tray seen from a front side; 
         FIG. 10  is a view of a tray portion seen from the rear side, in the state where the MP tray is closed; 
         FIG. 11  is a perspective view of the laser printer showing a state where a front cover is opened; and 
         FIG. 12  is a perspective view of the laser printer showing a state where a process cartridge is drawn out. 
     
    
    
     DETAILED DESCRIPTION 
     An aspect of the present invention will be described with reference to  FIGS. 1 to 12 . 
     1. General Configuration 
       FIG. 1  is a side sectional view of a laser printer according to an aspect of an image forming apparatus. The laser printer  1  includes a feeder section  4 , which serves to feed a paper sheet  3  (a sheet member) that is a recording medium, and an image formation section  5  which serves to form an image on the fed paper sheet  3 , within a body casing  2  (a housing). 
     (1) Body Casing 
     An attachment/detachment opening  6  for attaching and detaching a process cartridge  18 , described later, is formed in a side wall on one side (one side surface) of the body casing  2 . The body casing  2  is provided with a front cover  7  for opening and closing the attachment/detachment opening  6 . 
     The front cover  7  is rotatably supported by a cover shaft, not shown, which is inserted through the lower end part thereof. Thus, when the front cover  7  is closed about the cover shaft, the attachment/detachment opening  6  is closed by the front cover  7  as shown in  FIG. 1 . When the front cover  7  is opened or inclined with the cover shaft as a fulcrum, the attachment/detachment opening  6  is opened, and the process cartridge  18  can be attached to and detached from the body casing  2  through the attachment/detachment opening  6 . 
     Incidentally, regarding the laser printer  1  and the process cartridge  18  that includes a development cartridge  27 , described later, a side on which the front cover  7  is provided is referred to as a “front side”, and the opposite side is referred to as a “rear side”. Besides, a right side (far side of  FIG. 1 ) of the laser printer  1  viewed from its front surface side is referred to as a “right side”, and the opposite side (near side of  FIG. 1 ) is referred to as a “left side”. 
     (2) Feeder Section 
     The feeder section  4  includes a feed tray  8  (sheet member accommodation cassette), which is detachably mounted at a bottom part of the body casing  2 , and a separation roller  9  and a separation pad  10 , which are disposed over the front end part of the feed tray  8 . The feeder section  4  further includes a feed roller  11 , which is disposed on the rear side of the separation roller  9  (on the upstream side of the conveyance direction of the paper sheet  3  with respect to the separation pad  10 ). 
     The feeder section  4  is provided with a paper dust removal roller  12 , which is arranged above the front side of the separation roller  9  (on the downstream side of the conveyance direction of the paper sheet  3  with respect to the separation roller). An opposition roller  13  is arranged in opposition to the paper dust removal roller  12 . In addition, a first conveyance path  14  (a first conveyance passage) of the paper sheet  3  has a shape in which the paper sheet  3  is folded back rearwards in the shape of letter U from near the arrangement position of the paper dust removal roller  12 . On the further downstream side of the conveyance direction, registration rollers  15  and  15  being a pair of rollers are arranged under the process cartridge  18 . 
     A sheet urging plate  16  on which the paper sheets  3  can be placed in stacked fashion is included inside the feed tray  8 . The sheet urging plate  16  is swingably supported at its rear end part, whereby its front end part is movable in up and down directions. 
     A lever  17  for lifting the front end part of the sheet urging plate  16  upwards is disposed at the front end part of the feed tray  8 . The lever  17  has its rear end part swingably supported by a lever shaft, not shown, at a position under the front end part of the sheet urging plate  16 , and its front end part abuts against the front end part of the lower surface of the sheet urging plate  16 . Thus, when a rotational drive force, which is counterclockwise as viewed in the figure, is inputted to the lever shaft, the lever  17  is rotated with a fulcrum at the lever shaft, and the front end part of the lever  17  lifts up the front end part of the sheet urging plate  16 . 
     When the front end part of the sheet urging plate  16  is lifted up, the uppermost ones of the paper sheets  3  on the sheet urging plate  16  are pressed by the feed roller  11 , and they begin to be fed toward the separation position between the separation roller  9  and the separation pad  10 , by the rotation of the feed roller  11 . 
     On the other hand, when the feed tray  8  is detached from the body casing  2 , the rotational drive force input is released, and the front end part of the sheet urging plate  16  moves down by the weight of this front end part itself so as to assume a state where the sheet urging plate  16  extends along the bottom surface of the feed tray  8 . In this state, the paper sheets  3  can be placed on the sheet urging plate  16  in the stacked fashion. 
     When interposed between the separation roller  9  and the separation pad  10  by the rotation of this separation roller  9 , the paper sheets  3  delivered toward the separation position by the feed roller  11  are reliably separated one by one and are fed. The fed paper sheet  3  is folded back along the first conveyance path  14 , which is U-shaped. Specifically, the fed paper sheet  3  is first conveyed frontward and then obliquely upwards by the separation roller  9  and the separation pad  10 . The paper sheet  3  further passes through between the paper dust removal roller  12  and the opposition roller  13 , thereby the paper dust is removed. The paper sheet  3  is thereafter conveyed to the registration rollers  15 . 
     The registration rollers  15  are configured as a pair of rollers opposing to each other. After registration of the paper sheet  3 , the registration rollers  15  convey this paper sheet  3  toward a transfer position of the image formation section  5 . The transfer position is the nip position between a photosensitive drum  28  and a transfer roller  30 , described later. A toner image on the photosensitive drum  28  is transferred onto the paper sheet  3  at this transfer position. 
     (3) Image Formation Section 
     The image formation section  5  includes a scanner unit  19 , the process cartridge  18 , a fixing unit  20 , etc. 
     (a) Scanner Unit 
     The scanner unit  19  is disposed at an upper part within the body casing  2 . The scanner unit  19  includes a laser light source (not shown), a polygon mirror  21  which is driven to rotate, an fθ lens  22 , a reflector  23 , a lens  24 , a reflector  25 , etc. As indicated by broken lines in  FIG. 1 , a laser beam based on image data emitted from the laser light source is deflected by the polygon mirror  21  and is passed through the fθ lens  22 . Thereafter, the laser beam is folded back rearwards by the reflector  23  and is further passed through the lens  24 . Thereafter, the laser beam is bent rearwards and obliquely downwards by the reflector  25 . In this way, the laser beam is projected onto the surface of the photosensitive drum  28  of the process cartridge  18  by fast scan. 
     (b) Process Cartridge 
     The process cartridge  18  is detachably attached to the body casing  2  under the scanner unit  19 . This process cartridge  18  includes a drum cartridge  26  and a development cartridge  27  that is detachably mounted on the drum cartridge  26 . 
     The drum cartridge  26  has the development cartridge  27  mounted on its front side. The drum cartridge  26  includes on the rear side thereof the photosensitive drum  28 , a scolotron type electric charger  29 , the transfer roller  30  and a cleaning brush  31 . 
     Among these constituents, the scolotron type charger  29  is arranged in opposition to the photosensitive drum  28  with a predetermined spacing between the charger  29  and drum  28 . The charger  29  can uniformly charge the surface of the photosensitive drum  28  to the positive polarity. 
     The development cartridge  27  is provided with a toner accommodation chamber  32  in which a toner is accommodated, a supply roller  33 , a development roller  34  and a layer thickness regulation blade  35 . 
     The toner within the toner accommodation chamber  32  is supplied toward the supply roller  33  by an agitator  36 , which is driven to rotate, and is supplied to the development roller  34  by the rotation of the supply roller  33 . On this occasion, the toner is frictionally charged positively between the supply roller  33  and the development roller  34 . The toner supplied onto the development roller  34  advances into the interspace between the layer thickness regulation blade  35  and the development roller  34 , in accordance with the rotation of this development roller  34 . The toner is then carried on the development roller  34  in the form of a thin layer of predetermined thickness. 
     As the photosensitive drum  28  is rotated, the surface thereof is first positively charged uniformly by the scolotron type charger  29 . Thereafter, the surface of the photosensitive drum  28  is exposed to light by the fast scan with the laser beam from the scanner unit  19 . Thus, the surface of the photosensitive drum  28  is formed with an electrostatic latent image, which corresponds to an image to be formed on the paper sheet  3 . 
     Subsequently, when the toner carried on the development roller  34  and charged positively is opposed and touched to the photosensitive drum  28  by the rotation of the development roller  34 , the toner is supplied to the electrostatic latent image, which has been formed on the surface of the photosensitive drum  28 . In other words, the toner is supplied to an exposed part, which has been exposed to the light by the laser beam and whose potential is lower, in the surface of the photosensitive drum  28  positively charged uniformly. Thus, the electrostatic latent image of the photosensitive drum  28  is turned into a visible image, and the toner image based on a reversal development is carried on the surface of the photosensitive drum  28 . 
     Thereafter, the toner image carried on the surface of the photosensitive drum  28  is transferred onto the paper sheet  3  by a transfer bias applied to the transfer roller  30 , while the paper sheet  3  conveyed by the registration rollers  15  passes through the transfer position between the photosensitive drum  28  and the transfer roller  30  as shown in  FIG. 1 . The paper sheet  3  on which the toner image has been transferred is conveyed to the fixing unit  20 . Incidentally, a transfer remainder toner, which remains on the photosensitive drum  28  after the transfer, is recovered onto the development roller  34 . Besides, paper dust that adheres on the photosensitive drum  28  from the paper sheet  3  is collected by the cleaning brush  31  after the transfer. 
     (c) Fixing Unit 
     The fixing unit  20  is disposed on the rear side of the process cartridge  18 . The fixing unit  20  includes a heating roller  37  and a pressing roller  38 . 
     The heating roller  37  includes a halogen lamp for heating. The heating roller  37  is driven and rotated by power inputted from a motor not shown. The pressing roller  38  is arranged in opposition to and below the heating roller  37  so as to press this heating roller  37 . The pressing roller  38  is driven in accordance with the rotation of the heating roller  37 . 
     The fixing unit  20  is disposed behind the process cartridge  18  and on the downstream side of the conveyance direction of the paper sheet  3 . The fixing unit  20  includes the heating roller  37 , the pressing roller  38  and a conveyance roller  39 . The heating roller  38  has the halogen lamp as a heater provided in a tube made of metal. The pressing roller  38  is arranged in opposition to and below the heating roller  37  and is disposed so as to press the heating roller  37  from below. Besides, the conveyance roller  39  is disposed on the downstream side of the conveyance direction of the paper sheet  3  with respect to the heating roller  37  and the pressing roller  38 . 
     The toner transferred on the paper sheet  3  is thermally molten and fixed onto the paper sheet  3  while this paper sheet  3  passes between the heating roller  37  and the pressing roller  38 . The paper sheet  3  is guided by the conveyance roller  39  so as to be folded back in the shape of letter U by a guide portion  40 , which is vertically arranged behind this conveyance roller  39 . The paper sheet  3  is conveyed toward sheet discharge rollers  40   a . Thereafter, the paper sheet  3  is discharged onto a sheet discharge tray  40   b  by the sheet discharge rollers  41 . 
     2. Multipurpose Mechanism 
       FIG. 2  is a side sectional view showing a state where a multipurpose tray (a loading tray), hereinafter referred to as an MP tray  41 , is opened. In addition to the paper feed mechanism in which the paper sheet  3  is conveyed from the feed tray  8  to the transfer position through the first conveyance path  14 , the laser printer  1  has a multipurpose mechanism (hand-insertion feed mechanism) in which a paper sheet is conveyed from the front surface side of the laser printer  1  to the transfer position by hand insertion. 
     In other words, the feeder section  4  includes the MP tray  41  and a multipurpose feed mechanism unit (a feed-in mechanism), hereinafter referred to as an MP feed mechanism unit  42 , for feeding the paper sheet  3  on the MP tray  41 . 
     (1) MP Tray 
     A rectangular opening  7   a  (a sheet member feed-in port) is penetratingly formed in the front cover  7 , and the MP tray  41  is disposed so as to cover the rectangular opening  7   a . The MP tray  41  includes a cover portion  43 , which constitutes the front wall of the body casing  2 , and a tray portion  44  on which the paper sheets  3  for the hand insertion are loaded. As shown in  FIG. 2 , a lower end side of the cover portion  43  is supported on the body casing  2  through a rotary shaft  43   a . The cover portion  43  is openable and closable about the rotary shaft  43   a . The cover portion  43  is held in a state where its inner surface part  43   b  faces up. The tray portion  44  is mounted on the inner surface part  43   b.    
     The tray portion  44  includes a first tray plate  45 , which is arranged on the inner surface part  43   b  of the cover portion  43 , and a second tray plate  46 , which is rotatably supported on a front end part of the first tray plate  45 . The first tray plate  45  is located at a position at which it is received in the inner surface part  43   b  of the cover portion  43  in the closed state (refer to  FIG. 1 ) of the MP tray  41 . The first tray plate  45  is slidable to a position at which its front end part protrudes in front of the cover portion  43  along a guide groove  47 , in the opened state (refer to  FIG. 2 ) of the MP tray  41 . 
     The second tray plate  46  is rotatably supported on the front end part of the first tray plate  45  and is rotatable between a position at which it is placed on the upper surface of the first tray plate  45  (refer to  FIG. 1 ), and a position at which it is spread in front of the first tray plate  45  (refer to  FIG. 2 ). By the way, in the opened state of the MP tray  41  as shown in  FIG. 2 , the tray portion  44  assumes an attitude in which the side of the rotary shaft  43   a  (the insertion distal-end side of the paper sheet  3 ) inclines downward. 
     The MP tray  41  is provided with a guide mechanism  49  having a pair of guide ribs  48  and  48  (only the left one of them is shown in  FIG. 1  or  FIG. 2 ) between which both the widthwise ends of the paper sheets  3  loaded on the tray portion  44  are held so as to guide the conveyance of the paper sheet  3  when this MP tray  41  is opened. The pair of guide ribs  48  and  48  are slidable between positions at which they come near to each other and positions at which they come away from each other, whereby the MP tray  41  can stack the paper sheets  3  of any desired size in the stacked fashion. 
     The guide mechanism  49  is disposed so as to lie behind the upper end part of the folded up tray portion  44  (in a space over the MP feed mechanism unit  42 ), in the closed state of the MP tray  41  (refer to  FIG. 1 ). The guide mechanism  49  slides and moves along a guide groove  50  and lies on the rear end side of the first tray plate  45 , in the opened state of the MP tray  41  (refer to  FIG. 2 ). 
     (2) MP Paper Feed Mechanism Unit 
     As shown in  FIG. 2 , the MP feed mechanism unit  42  includes a multipurpose feed roller (feed-in roller), hereinafter referred to as an MP feed roller  51 , a multipurpose separation roller, hereinafter referred to as an MP separation roller  52 , and a multipurpose separation pad (separation member), hereinafter referred to as an MP separation pad  53 . The MP separation pad  53  is opposed to and pressed against the MP separation roller  52 . In a state where the MP separation roller  52  and the MP separation pad  53  touch in opposition to each other, the MP separation pad  53  is pressed against the MP separation roller  52  by the urging force of an urging member (not shown). That is, the multipurpose mechanism in this aspect is a twin-roller type in which the MP feed roller  51  and the MP separation roller  52  are provided. The multipurpose mechanism has a configuration in which the MP feed roller  51  is arranged on the side of the MP tray  41  and the separation roller  52  is arranged behind the MP feed roller  51 . 
     The uppermost ones of the paper sheets  3  stacked on the MP tray  41  are fed by the rotation of the MP feed roller  51  and are held between the MP separation roller  52  and the MP separation pad  53 , whereupon they are separated and fed one by one by the cooperation of these constituents  52  and  53 . The fed paper sheet  3  passes through a second conveyance path  54  (a second conveyance passage). The paper sheet  3  advances from a junction point X near the downstream end of the first conveyance path  14  in the conveyance direction until it is fed to the side of the registration rollers  15 . 
     More specifically, a partition member  55 , which is held between the first conveyance path  14  and the second conveyance path  54 , defines a side sectional shape extending along the U-shape of the first conveyance path  14 . The partition member  55  is in a shape in which it inclines from the junction point X, being the highest position, downwards toward the front side thereof. In short, a space on the upper surface side of the partition member  55  is a downwardly inclining space that extends downwards from the junction point X toward the front side. Besides, a roller unit  56 , in which the MP feed roller  51  and the MP separation roller  52  are supported by shafts in a state where they are exposed below, is disposed in the downwardly inclining space, and the MP feed roller  51  is moved up and down within the downwardly inclining space as will be stated later. 
     The MP separation pad  53  is arranged on the intermediate part of the inclining upper surface of the partition member  55 . The MP separation roller  52  is arranged in opposition to the MP separation pad  53  from above, whereby both the constituents  52  and  53  are in the pressed state. More specifically, an opposition position Y, at which the MP separation roller  52  and the MP separation pad  53  oppose, lies on the rear side with respect to the frontmost part Z (a part nearest to one side surface) of the first conveyance path  14  and on the front side with respect to the junction point X. Moreover, the opposition position Y lies below the junction point X and above the frontmost part Z. 
       FIG. 3  is a perspective view of the partition member  55  seen from the rear side thereof. One or more (in this aspect, three) common rolls  57 , which are arrayed in a right-and-left direction and are supported by shafts so as to be idly turnable, are provided at the uppermost end part of the partition member  55 , namely, the position thereof corresponding to the junction point X. The common rolls  57  have their outer peripheral surfaces exposed so as to touch the paper sheet  3  conveyed from both the first conveyance path  14  and the second conveyance path  54  and to turn with the advance of the paper sheet  3 . 
     (3) Vertical Movement Drive Mechanism of MP Feed Roller 
       FIGS. 4 and 5  are perspective views showing a vertical movement drive mechanism  60  (a drive mechanism) of the MP feed roller  51 . In each of these figures, the left upper side of the drawing is the front side of the laser printer  1 , the right downward direction of the drawing is the conveyance direction of the paper sheet  3 , the right side of the drawing is the left side of the laser printer  1 , and the left side of the drawing is the right side of the laser printer  1 . Besides,  FIGS. 6 and 7  are left side views of the vertical movement drive mechanism. In each of these figures, the right side of the drawing is the front side of the laser printer  1 , and the left direction of the drawing is the conveyance direction of the paper sheet  3 . 
     As shown in  FIGS. 4 and 5 , the roller unit  56  is so configured that the MP feed roller  51  and the MP separation roller  52  are rotatably mounted in a common bearing member  61 . Specifically, the MP feed roller  51  is coaxially and unitarily provided with a gear  62  on its side (the left side, and the right side of the drawing in each of the figures), and the constituents  51  and  62  are rotatably supported by a shaft on the front end side of the bearing member  61 . The MP separation roller  52  is also coaxially and unitarily provided with a gear  63  on its side (the left side), and the constituents  52  and  63  are rotatably supported by a shaft on the rear end side of the bearing member  61 . Besides, the gears  62  and  63  are connected through an intermediate gear  64 . 
     A rotary shaft member  65  extending in the right-and-left direction is arranged coaxially with the MP separation roller  52  on the left side of the MP separation roller  52 . A rotary shaft of the MP separation roller  52  is fixed to the right end part of the rotary shaft member  65 , while a separation roller drive gear  66  is fixed to the left end part of the rotary shaft member  65 . Thus, a drive force from a driving motor not shown is exerted on the separation roller drive gear  66 , whereby the MP separation roller  52  is rotated, and the MP feed roller  51  is consequently rotated in driven fashion. Besides, the roller unit  56  is so configured that the side of the MP feed roller  51  is swingable about the MP separation roller  52 . 
     A support arm  67  is arranged so as to extend along the right-and-left direction of the laser printer  1 , above the rotary shaft member  65 . The support arm  67  is disposed so as to be rotatable about a rotary shaft (not shown) extending along a vertical direction at its middle position. In addition, a penetrating hole  67   a  which vertically penetrates through the support arm  67  is formed on the side of one side end part (the side of the right end part) of this support arm  67 . A protrusion  61   a , which is protruded on the rear end side of the upper surface of the bearing member  61 , is inserted in the penetrating hole  67   a.    
     A pressing member  68  is disposed behind the side of the other end part (the side of the left end part) of the support arm  67 , in such a manner that an upper end part of the pressing member  68  is tiltable about its lower end part. Further, as shown in  FIG. 4 , the pressing member  68  abuts on the left end part of the support arm  67  with an upper end part of the pressing member  68  located at a front position. The pressing member  68  presses the support arm  67  frontward. On this occasion, the right end part of the support arm  67  presses the protrusion  61   a  rearwards, whereby the MP feed roller  51  lies at its ascent position, which is spaced from the upper surface of the partition member  55  (refer also to  FIG. 2 ). 
     In contrast, in a state where the upper end part of the pressing member  68  is located at a rear position as shown in  FIG. 5 , the upper end part comes away from the left end part of the support arm  67 . Thus, the rearward pressing on the protrusion  61   a  by the right end part of the support arm  67  is released, and the MP feed roller  51  is moved by its own weight to its descent position at which it is abuttable on the upper surface of the partition member  55 , so that the paper feed of the paper sheet  3  is permitted. In this aspect, the MP feed roller  51  is at the same height as the MP separation roller  52  when the MP feed roller  51  is at the uppermost position (ascent position), as shown in  FIG. 2 . The MP feed roller  51  becomes lower than the MP separation roller  52  in a state where the MP separate roller  52  lies at the descent position. 
     Arranged in the vicinity of the pressing member  68  are a solenoid switch  69 , a sector gear  70 , and an input gear  71  that is rotated by receiving a drive force from a driving motor (not shown). 
     The solenoid switch  69  functions as a switch unit which performs an ON operation each time a feed start signal is received. A solenoid lever  72  has its substantially middle position  72   a  supported so as to be rotatable, and its front end part is lowered down by the ON operation of the solenoid switch  69 . Besides, the rear end part of the solenoid lever  72  is unitarily provided with an engagement pawl  72   b , which engages an engagement protrusion  70   a  protruded on the outer peripheral surface of the sector gear  70 . 
     The sector gear  70  includes a first cam  74  (a cam), a first lacked-tooth gear  75 , a second lacked-tooth gear  76  and a second cam  77 , which are rotated integrally with an identical rotary shaft  73 . 
     (a) First Lacked-Tooth Gear 
     More specifically, as shown in  FIG. 6 , the first lacked-tooth gear  75  has a part lacking teeth. The first lacked-tooth gear  75  is driven and rotated by meshing with the input gear  71  to which the drive force from the driving motor is inputted. Here, adjustments are made so that, when the engagement pawl  72   b  of the solenoid lever  72  and the engagement protrusion  70   a  of the sector gear  70  are in engagement, the lacked-tooth part of the first lacked-tooth gear  75  opposes the input gear  71 . That is, on this occasion, the drive force from the input gear  71  is not transmitted to the sector gear  70  (refer to  FIGS. 4 and 6 ). 
     (b) Second Lacked-Tooth Gear 
     The second lacked-tooth gear  76  is arranged on the left side of the first lacked-tooth gear  75  (in the right upper direction of the drawing in each of  FIGS. 4 and 5 , and in the far direction of the drawing in each of  FIGS. 6 and 7 ). The teeth of the second lacked-tooth gear  76  are lacking over a range of substantially one-third of its whole circumstance. The second lacked-tooth gear  76  functions to drive and rotate the MP separation roller  52 , by meshing with the separation roller drive gear  66 . In the state of  FIGS. 4 and 6 , the second lacked-tooth gear  76  has not meshed with the separation roller drive gear  66  yet, and the MP separation roller  52  is idly rotatable. 
     (c) Second Cam 
     The second cam  77  is arranged on the left side of the second lacked-tooth gear  76  (the right upper direction of the drawing in each of  FIGS. 4 and 5 , and the far side of the drawing in each of  FIGS. 6 and 7 ). The second cam  77  has a section orthogonal to the rotary shaft  73  that is substantially in the shape of letter D as a whole. One end part of the flat part  77   a  of this second cam  77  forms a protruded large-diameter part  77   b . A sector spring  78  is disposed in the vicinity of the second cam  77 . The sector spring  78  touches the large-diameter part  77   b  of the second cam  77  in a pressed condition in the state shown in  FIG. 6 . When the engagement by the solenoid lever  72  is released by the ON operation of the solenoids witch  69 , the sector spring  78  functions to forcibly rotate the second cam  77  in a clockwise direction in  FIG. 6  and turns the sector gear  70  to a position at which the first lacked-tooth gear  75  and the input gear  71  mesh with each other. 
     (d) First Cam 
     The first cam  74  is arranged on the right side of the first lacked-tooth gear  75  (the left lower direction of the drawing in each of  FIGS. 4 and 5 , and the near side of the drawing in each of  FIGS. 6 and 7 ). The first cam  74  has a large-diameter part  74   a  that is enlarged over a range about one-third of its whole circumference. With respect to  FIGS. 6 and 7 , the upper end part of the pressing member  68  is arranged at the near side of the first cam  74 . In the state of  FIGS. 4 and 6 , the large-diameter part  74   a  of the first cam  74  abuts on the upper end part of the pressing member  68  and holds this upper end part at the front position thereof. 
     Next, the operation of the vertical movement drive mechanism  60  of the MP feed roller  51  will be described. Before the feed start signal is applied to the solenoid switch  69 , this vertical movement drive mechanism  60  assumes a home position as shown in  FIGS. 4 and 6 . That is, the MP feed roller  51  lies at the ascent position spaced from the paper sheet  3 , and the MP separation roller  52  is in the idly rotatable state without being given the drive force. 
     When the feed start signal is applied to the solenoid switch  69  (outset of the feed-in operation of the sheet member), the engagement between the engagement protrusion  70   a  and the engagement pawl  72   b  is released as shown in  FIGS. 5 and 7 , so that the sector gear  70  is turned by the urging force of the sector spring  78  to the position at which the first lacked-tooth gear  75  and the input gear  71  mesh with each other. Thus, the sector gear  70  is driven and rotated clockwise in  FIG. 7 . On this occasion, the large-diameter part  74   a  of the first cam  74  retreats rearwards, and the engagement of the pressing member  68  is released, so that the MP feed roller  51  is moved by its own weight to the descent position at which it abuts on the upper surface of the paper sheet  3  lying on the upper surface of the partition member  55  (refer to  FIG. 5 ). However, the second lacked-tooth gear  76  and the separation roller drive gear  66  do not mesh with each other yet, and the MP separation roller  52  is idly rotatable. 
     Thereafter, the sector gear  70  is rotated still further, whereby the second lacked-tooth gear  76  and the separation roller drive gear  66  mesh with each other, so that the MP separation roller  52  is driven to rotate. Consequently the MP feed roller  51  is driven. Thus, the paper feed of the paper sheets  3  on the MP tray  41  is started, and these paper sheets  3  are separated one by one at the opposition position Y between the MP separation roller  52  and the MP separation pad  53 , so that the separated paper sheet  3  passes through the second conveyance path  54 . 
     When the sector gear  70  is rotated to the position at which the large-diameter part  74   a  of the first cam  74  abuts on the upper end part of the pressing member  68  again, the left end part of the support arm  67  is gradually pressed against the front side by the pressing member  68  until the MP feed roller  51  is reset to the ascent position. On this occasion, the second lacked-tooth gear  76  and the separation roller drive gear  66  still mesh with each other, and the MP separation roller  52  and the MP feed roller  51  are driven to rotate. Here, the circumferential length of the large-diameter part  74   a  of the first cam  74  is adjusted so that the MP feed roller  51  is reset to the ascent position at a time before the rear end of the separated paper sheet  3  passes through the opposition position Y. Especially in this aspect, the timing is set on the basis of the length in the conveyance direction, of the paper sheet of the smallest size for use in the laser printer  1  (for example, the length of the shorter side of a postal card). 
     (4) Paper-Sheet Presence/Absence Sensor 
       FIGS. 8A and 8B  are perspective views showing a paper-sheet presence/absence sensor  90 . In these figures, the right lower side of the drawing is the front side of the laser printer  1 , and the left upper direction of the drawing is the conveyance direction of the paper sheet  3 . 
     The paper-sheet presence/absence sensor  90  detects the presence or absence of the paper sheet  3  whose distal end lies on the rear side (downstream side of the conveyance direction) with respect to the lower position of the MP feed roller  51  (the position of this roller  51  opposing to the upper surface of the partition member  55 , that is, the position thereof abutting on the paper sheet  3  in the presence of this paper sheet  3 ). 
     Specifically, the paper-sheet presence/absence sensor  90  includes a swing member  91 , the upper end side of which is supported on a rotary shaft extending along a right-and-left direction and the lower end side of which is made swingable. The sensor also includes a light shield member  92 , which is rotatable about a rotary shaft similarly extending along the right-and-left direction (located on the rear side with respect to the rotary shaft of the swing member  91 ), and a photoelectric sensor  93  of so-called “transmission type”. 
     The swing member  91  is formed with a guide groove  94 , which extends from the upper end thereof toward the lower end side thereof. The swing member  91  defines a sectoral shape in a side view, as a whole. The top part of the sectoral member  91  is supported by the rotary shaft. The light shield member  92  defines a rod-like shape extending in the right-and-left direction, as a whole. An arm  95  is provided at one end part of the rod-like member  92  so as to protrude along a radial direction. The distal end  95   a  of the arm  95  is bent at right angles and is then inserted into the guide groove  94  of the swing member  91 . The bent part of the distal end  95   a  is movable along the guide groove  94 . A light shield plate  96  is provided at the other end part of the light shield member  92  so as to protrude in the radial direction. The protrusion length of the light shield plate  96  from the rotary shaft thereof is made smaller than that of the swing member  91  from the rotary shaft thereof. The photoelectric sensor  93  includes a light projection element  93   a  and a light reception element  93   b , which are arranged in opposition so as to hold the swing path of the light shield plate  96  therebetween in the right-and-left direction. 
     Owing to such a configuration, when the paper sheet  3  does not lie at the lower position W of the MP feed roller  51  (the opposition position between the MP feed roller  51  and the upper surface of the partition member  55  or abutment position between the feed-in roller and the sheet member) as shown in  FIG. 8A , the swing member  91  hangs down by its own weight, and the light shield member  92  assumes an attitude in which the arm  95  lies at the lowermost end part of the guide groove  94  by the weight of this arm  95  itself. On this occasion, the light shield plate  96  lies out and frontward of the opposition position between the light projection element  93   a  and the light reception element  93   b , and the photoelectric sensor  93  is in a light input state. 
     On the other hand, when the distal end of the paper sheet  3  has come onto the downstream side of the conveyance direction of this paper sheet  3  with respect to the lower position W, as shown in  FIG. 8B , that is, when the paper sheet  3  has come onto the downstream side of the conveyance direction to the position at which the upper surface of this paper sheet  3  abuts on the MP feed roller  51  lying at the descent position thereof, the front end surface of the swing member  91  is pushed and rotated rearwards by the distal end of the paper sheet  3 . Consequently, while the distal end part of the arm  95  is being guided from the lowermost end part of the guide groove  94  to the uppermost end part thereof, the light shield member  92  is rotated, and the light shield plate  96  is moved to the opposition position between the light projection element  93   a  and the light reception element  93   b , so that the photoelectric sensor  93  falls into a light-shielded state. 
     3. Attachment/Detachment Passage for Process Cartridge 
       FIG. 9  is a perspective view of the roller unit  56  and the MP tray  41  seen from the front side.  FIG. 10  is a view of the tray portion  44  seen from the rear side, in the state where the MP tray  41  is closed. 
     The roller unit  56  defines a shape in which the middle part thereof including the MP feed roller  51 , the MP separation roller  52 , etc. protrudes frontward. A cut-away part  46   a  is formed in that distal-end middle part of the second tray plate  46 , which corresponds to the protrusive part  56   a . Thus, as shown in  FIG. 1 , when the MP tray  41  is closed, the protrusive part  56   a  of the roller unit  56  can be received in the cut-away part  46   a , and the size of the laser printer  1  in the front-and-rear direction thereof can be reduced. 
     As shown in  FIG. 1 , the upper surface of the roller unit  56  defines a shape which inclines down rearwards. A space over the inclining upper surface is an attachment/detachment passage  100  which communicates with the attachment/detachment opening  6  of the process cartridge  18 . 
       FIG. 11  is a perspective view of the laser printer  1  showing a state where the front cover  7  is opened.  FIG. 12  is a perspective view of the laser printer  1  showing a state where the process cartridge  18  is drawn out. 
     In the state where the process cartridge  18  is attached to the body casing  2  as shown in  FIG. 11 , it is arranged so that the lower part of the process cartridge  18  overlaps the roller unit  56  behind this roller unit, as viewed from the front surface side of the laser printer  1 . Accordingly, the attachment/detachment passage  100  defines a shape in which the vicinity of the attachment/detachment opening  6  is bulged by the roller unit  56 . Therefore, the process cartridge  18  is attached or detached in a manner by lifting the cartridge over the roller unit  56 . 
     In this aspect, as shown in  FIGS. 11 and 12 , when the front cover  7  is opened, not only the front surface side of the body casing  2 , but also the upper front end part thereof is opened. Thus, the process cartridge  18  can be attached or detached by lifting the cartridge over the roller unit  56 . 
     4. Advantages of this Embodiment 
     (1) With the configuration of JP-A-2005-41652 wherein paper feed and separation are performed by one multipurpose feed roller, the multipurpose feed roller of comparatively large diameter needs to be arranged in the vicinity of a multipurpose tray. In contrast, in this aspect, the twin-roller scheme consisting of the MP feed roller  51  and the MP separation roller  52  has been adopted for the multipurpose mechanism. Thus, it has been permitted to adopt rollers that are smaller in diameter than the multipurpose feed roller, as both the rollers  51  and  52 . Besides, while the MP feed roller  51  for performing the paper feed has been left in the vicinity of the MP tray  41 , the MP separation roller  52  has been arranged on the rear side, and the opposition position Y between the MP separation roller  52  and the MP separation pad  53  has been located between the junction point X and the frontmost part Z. 
     Thus, the size of the laser printer  1  in the horizontal direction thereof can be reduced to the extent that the MP feed roller  51  for performing the paper feed is smaller in diameter than the multipurpose feed roller in the prior art. 
     (2) Further, in this aspect, owing to the configuration in which the opposition position Y lies below the junction point X, the size of the laser printer  1  in the vertical direction thereof can also be reduced. 
     (3) In the configuration of this aspect, the MP feed roller  51  is located by the vertical movement drive mechanism  60  at the descent position allowing the paper sheet  3  to be fed, at the outset of the paper feed operation in which the paper feed start signal has been applied to the solenoid switch  69 , and the MP feed roller  51  is thereafter reset to the ascent position before the rear end of the paper sheet  3  passes through the opposition position Y. Accordingly, even in a case, for example, where one remaining paper sheet  3  on the MP tray  41  is to be fed, the rotational drive of the MP feed roller  51  with the abutment thereof on the upper surface of the partition member  55  is avoided, and the burning of the MP feed roller  51  and a heavy load on the vertical movement drive mechanism  60  are preventable. Moreover, since the reset timing of the MP feed roller  51  is set on the basis of the paper sheet  3  of the smallest size usable by the laser printer  1 , the above drawbacks are preventable for the paper sheet  3  of any size. 
     (4) The common rolls  57  are disposed at the distal end part of the partition member  55  on the side of the junction point X, whereby the paper sheet  3  coming via both the first and second conveyance paths  14  and  54  can be guided, and decrease in the number of components, in turn, reduction in the size of the apparatus can be attained. 
     (5) The vertical movement drive mechanism  60  has the comparatively simple configuration which includes the first cam  74 , pressing member  68  and support arm  67 , and in which the MP feed roller  51  is moved up and down by the rotation of the first cam  74 . Moreover, the first cam  74  is disposed coaxially and unitarily with the second lacked-tooth gear  76  which meshes with the separation roller drive gear  66  for turning the MP separation roller  52  and the MP feed roller  51 . Accordingly, the vertical movement timing of the MP feed roller  51  can be easily set by adjusting the circumferential length of the large-diameter part  74   a  of the first cam  74  on the basis of the second lacked-tooth gear  76 . 
     (6) The MP feed roller  51  is moved up and down between the ascent position and the descent position, with the highest position being substantially the same height as that of the MP separation roller  52 , within the downwardly inclining space which spreads down frontward from the junction point X, and on this side of the frontmost part Z of the second conveyance path  54 . In this manner, the downwardly inclining space is effectively utilized, whereby enlargement in the size of the laser printer  1  in the vertical direction thereof can be suppressed. 
     (7) Besides, the configuration in which the MP feed roller  51  is driven relative to the MP separation roller  52  is simpler than a configuration in which these rollers are individually driven. 
     (8) In this aspect, the paper-sheet presence or absence sensor  90  has been configured so as to detect the paper sheet  3  whose distal end lies on the downstream side of the conveyance direction of the paper sheet with respect to the lower position W that is abuttable on the MP feed roller  51  of the descent position. With such a configuration, when the presence of the paper sheet has been detected by the paper-sheet presence or absence sensor  90 , the paper sheet  3  exists at the lower position W without fail. It is therefore preventable that, in the absence of the paper sheet  3 , the MP feed roller  51  is moved to the descent position to be driven and rotated. 
     (9) Further, the paper-sheet presence or absence sensor  90  has the configuration in which, in the absence of the paper sheet  3  at the lower position W, the light shield plate  96  brings the photoelectric sensor  93  to the position of the light input state by the weights of the swing member  91  and arm  95  themselves, and in which the swing member  91  is pushed by the paper sheet  3 , whereby the light shield plate  96  moves the photoelectric sensor  93  to the position of the light-shielded state. Accordingly, the simple configuration is realized without providing an urging member or the like. 
     (10) Moreover, the swing member  91  is disposed in the comparatively large region of the front side in the downwardly inclining space, while the light shield plate  96  which is narrower in swing range than the swing member  91  is disposed in the comparatively small region of the rear side, whereby the downwardly inclining space is similarly utilized effectively. 
     Other Embodiments 
     The present invention is not restricted to the aspect described above with reference to the drawings, but aspects as stated below by way of example shall be covered within the technical scope of the invention, and the invention can be variously altered and performed within a scope not departing from the purport thereof, otherwise than the following: 
     (1) In the foregoing aspect, the reset timing of the MP feed roller  51  to the ascent position has been set by the gear control based on the sector gear  70 , etc., but this configuration is not restrictive, and the reset timing may well be set by a software control. 
     (2) The paper-sheet presence or absence sensor  90  has included the photoelectric sensor  93  of transmission type, but a photoelectric sensor of so-called “reflection type” may well be utilized by replacing the light shield plate  96  with a reflection plate. Alternatively, any other detection sensor such as magnetic sensor may well be utilized. 
     As was described, according to an aspect of the invention, the opposition position between the separation member and the separation roller lies below the junction point. 
     According to the configuration, the opposition position between the separation member and the separation roller is located below the junction point, whereby the size of the whole image forming apparatus in the vertical direction thereof can also be reduced. 
     Further, the process unit is attached at a position at which it overlaps the feed-in mechanism behind the feed-in mechanism, as viewed from the side of one side surface; and that an attachment/detachment passage for attaching and detaching the process unit from the housing is formed over the feed-in mechanism. 
     According to the configuration, the feed-in mechanism is of the twin-roller scheme which consists of the feed-in roller and the separation roller, so that the height of the feed-in mechanism can be made low. Accordingly, even when the attachment/detachment passage for the process unit is provided over the paper feed mechanism, the inclination angle of the attachment/detachment passage in the horizontal direction thereof can be made gentle. 
     Further, the drive mechanism which moves the feed-in roller up and down is provided; wherein the drive mechanism brings the feed-in roller to a descent position at which the feed-in roller is abuttable on the sheet member at an outset of a feed-in operation for the sheet members on the loading tray, so as to start the feed-in, and it lifts the feed-in roller to an ascent position which is spaced from the sheet members, at a timing before a rear end of the sheet member fed in passes through an abutment position between the sheet member and the feed-in roller. 
     Also, the timing at which the feed-in roller is lifted is a timing before the rear end of a paper sheet of smallest size as can be loaded on the loading tray passes through the abutment position between the sheet member and the feed-in roller. 
     With a configuration in which a feed roller is always held at a position where the feed roller abuts on sheet members, in a case, for example, where only one sheet member exists on a loading tray, a feed-in roller might damage in such a manner that the feed-in roller abuts on the opposing member thereof after having fed in the sheet member, and that the feed-in roller is driven and rotated in this condition. With the configuration, the feed-in roller is lifted at the timing before the rear end of the sheet member passes through the abutment position between the sheet member and the feed-in roller. Besides, when the timing at which the feed-in roller is lifted is determined on the basis of the smallest size of the sheet members that can be loaded on the loading tray, the damage of the feed-in roller can be prevented even in case of feeding in sheet members of larger size. 
     Also, the feed-in roller is moved up and down on this side of a nearest part of the second conveyance passage, as viewed from the side of one side surface. 
     According to the configuration, the vertical movement range of the feed-in roller can be held wide while enlargement in the size of the image forming apparatus in the vertical direction thereof is suppressed. 
     Further, the feed-in roller is moved up and down at a position which is lower than the opposition position between the separation member and the separation roller. 
     According to the configuration, the feed roller is moved up and down at the position which is lower than the opposition position between the separation member and the separation roller, so that a space which is above the opposition position between the separation member and the separation roller need not be ensured for the vertical movement of the feed roller. Incidentally, further reduction in the size of the image forming apparatus in the vertical direction thereof is permitted. 
     Further, the feed-in roller is disposed so as to be vertically movable about the separation roller, and that it is gear-connected with the separation roller so as to rotate in driven fashion relative to the drive and rotation of the separation roller. 
     The configuration can be simplified more than a configuration in which the feed-in roller and the separation roller are driven and turned by separate drive sources. 
     Also, the drive mechanism is configured including a cam which is rotated by receiving a drive force from a driving motor; and a support arm one end part of which is held in engagement with a bearing member for bearing the feed-in roller, and the other end part of which abuts on the cam and moves the feed-in roller up and down with rotation of the cam. 
     According to the configuration, the drive mechanism which moves the feed-in roller up and down can be incarnated by the simple configuration based on a cam mechanism. 
     Further, common rolls whose outer peripheral surfaces are exposed to the first conveyance passage and the second conveyance passage and which guide the sheet member passing through both the conveyance passages are rotatably disposed at the junction point between the first and second conveyance passages. 
     According to the configuration, both the sheet member coming via the first conveyance passage and the sheet member coming via the second conveyance passage can be guided by the common rolls, whereby decrease in the number of components, in turn, reduction in the size of the apparatus can be attained. 
     Further, a detection mechanism which detects presence or absence of the sheet member on the loading tray is provided; wherein the detection mechanism detects the presence or absence of the sheet member on the loading tray, on the basis of the presence or absence of the sheet member at a position on the downstream side of the conveyance direction of the sheet member with respect to the abutment position between the feed-in roller and the sheet member. 
     With a configuration in which a detection position by a detection mechanism for detecting the presence or absence of a sheet member on a loading tray is set on this side of the conveyance direction of the sheet member with respect to the abutment position between a feed-in roller and the sheet member, a feed-in operation is started even in a case where the sheet member exists on the loading tray, but the sheet member does not exist at the abutment position between the feed-in roller and the sheet member. Then, the feed-in roller is driven and rotated in direct touch with the opposing member thereof, whereby unfavorably the feed-in roller damages or a large load is exerted on the drive system of the feed-in roller. In the configuration, therefore, the detection position by the detection mechanism is set on the downstream side of the conveyance direction of the sheet member with respect to the abutment position between the feed-in roller and the sheet member. With configuration, in a case where the presence of the sheet member on the loading tray has been detected by the detection mechanism, the sheet member exists at the abutment position thereof on the feed-in roller without fail, and hence, the feed roller can be prevented from being driven and rotated in the absence of the abutting sheet member. 
     Also, the detection mechanism includes a swing member which is supported by a shaft so as to be swingable about its upper end side, which usually hangs down by its own weight, to a position where its lower end part is abuttable on a front end of the sheet member that is fed in from the sheet member feed-in port, and which retreats from the second conveyance passage when pushed by the sheet member; and a detection unit for detecting the presence or absence of the sheet member on the basis of a swing position of the swing member. 
     According to the configuration, the swing member is usually in the state where it hangs down by its own weight, it is swung so as to retreat from the second conveyance passage when the lower end part is pushed by the sheet member, and the presence or absence of the sheet member is detected on the basis of the swing position. With the configuration, the detection mechanism can be incarnated by the comparatively simple configuration without providing, for example, an urging member. 
     Further, the detection unit is configured including a light shield member which is connected with the swing member through an arm on the downstream side of the conveyance direction of the sheet member with respect to the swing member, and which is swung with the swing of the swing member; and an optical type sensor which performs a detection operation on the basis of a light input state and a light-shielded state that change in accordance with a swing position of the light shield member. 
     The swing member needs to be disposed near the abutment position between the feed-in roller and the sheet member. In the configuration, therefore, the swing member is disposed near the abutment position, while the light shield member and the optical type sensor which constitute the detection unit are disposed on the downstream side of the conveyance direction of the sheet member, whereby enlargement in the size of the vicinity of the feed-in roller is suppressed. 
     Also, a swinging angle range of the light shield member is narrower than a swinging angle range in which the swing member is swung by being pushed by the sheet member. 
     According to the configuration, the swinging angle range of the light shield member is made narrow, whereby the size thereof on the downstream side of the conveyance direction of the sheet member is reduced. 
     Furthermore, the loading tray is disposed so as to be openable and closable between an open attitude in which the sheet members can be loaded and a closed attitude in which the loading tray extends along the side surface of the housing, and that it is formed with a cut-away part at its part which opposes to the feed-in mechanism in the closed attitude. 
     According to the configuration, in the closed attitude of the loading tray, the feed-in mechanism can be accommodated in the cut-away part, so that reduction in the size of the image forming apparatus in the horizontal direction thereof can be attained.