Abstract:
A medium stacking device includes a medium stacking part stacking a medium, and a first movement part movably provided with respect to the medium stacking part. The first movement part has a first medium restriction part restricting a position of the medium, and a first movement restriction parts including a plurality of restriction members, each of which engaging with the medium stacking part and restricting a direction of the movement of the first movement part.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is related to, claims priority from and incorporates by reference Japanese Patent Application No. 2011-181664, filed on Aug. 23, 2011. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to an image forming apparatus, especially relates to a configuration of a medium stacking device including a guide for a medium to be stacked. 
       BACKGROUND 
       [0003]    Conventionally, in such a medium stacking device, in order to regulate a position of a sheet in a width direction which is orthogonal to a carrying direction of the stacked sheet, two sheet guides have been disposed at the left and right of the sheet (see JP Laid-Open Patent Application No. H8-034525 (page 3,  FIG. 1 ). 
         [0004]    However, since the conventional sheet guide cannot completely prevent an incline of the guided medium, the medium is sometimes inclined with respect to the carrying direction. One of objects of the present invention is to eliminate the above mentioned problems by a simple configuration. 
       SUMMARY 
       [0005]    A medium stacking device of the present invention includes a medium stacking part stacking a medium, and a first movement part movably provided with respect to the medium stacking part. The first movement part has a first medium restriction part restricting a position of the medium, and a first movement restriction part including a plurality of restriction members, each of which engaging with the medium stacking part and restricting a direction of the movement of the first movement part. 
         [0006]    According to the present invention, the first movement part can minimize the incline of the medium which is being carried. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic configuration diagram of a main part configuration viewed from the front surface of an image forming apparatus of a first embodiment employing a medium stacking device according to the present invention. 
           [0008]      FIG. 2  is a configuration diagram viewed from the front surface (Y axis plus side) of a manual feed tray in the first embodiment. 
           [0009]      FIG. 3  is an external perspective view illustrating the configuration of the medium stacking device in the first embodiment. 
           [0010]      FIG. 4  is a configuration diagram viewed from the lower side of the medium stacking device in the first embodiment. 
           [0011]      FIG. 5  is an external perspective view illustrating a configuration of the surface (upper surface) of a medium stacking plate of the medium stacking device. 
           [0012]      FIG. 6  is an external perspective view illustrating a configuration of the rear surface (lower surface) of the medium stacking plate. 
           [0013]      FIG. 7  is an external perspective view illustrating a configuration of a sheet guide illustrated in  FIG. 3  in the first embodiment. 
           [0014]      FIG. 8  is a diagram excluding the medium stacking plate from the configuration diagram of  FIG. 4  in the first embodiment. 
           [0015]      FIG. 9  is a K-K cross-sectional view illustrating a cross-section along a position passing a center of screws illustrated in  FIG. 4  in the first embodiment. 
           [0016]      FIG. 10  is a size explanation diagram illustrating a position relationship between the sheet guide installed to the medium stacking plate and a pinion gear rotatably axially fixed to the medium stacking plate in the first embodiment. 
           [0017]      FIG. 11A  is a partially enlarged diagram for explaining an engagement position with a mesh of the pinion gear and a rack as an example in the first embodiment.  FIG. 11B  is a diagram illustrating another example of a mesh of the pinion gear and the rack in the first embodiment. 
           [0018]      FIG. 12  is a diagram used to an operation explanation of the sheet guide of the medium stacking device stacking recording sheets in the first embodiment. 
           [0019]      FIG. 13  is a configuration diagram viewed from the lower side of the medium stacking device in the second embodiment according to the present invention. 
           [0020]      FIG. 14  is an M-M cross-sectional view illustrating a cross-section along a position passing a center of screws shown in  FIG. 13 . The upper side of the medium stacking device is placed up. 
           [0021]      FIG. 15  is a diagram used to an operation explanation of the sheet guide of the medium stacking device stacking recording sheets in the second embodiment. 
           [0022]      FIG. 16  is a configuration diagram of the medium stacking device viewed from the lower side in the third embodiment according to the present invention. 
           [0023]      FIG. 17  is an external perspective view illustrating a configuration of a sheet guide in the third embodiment. 
           [0024]      FIG. 18  is an external perspective view illustrating a configuration of a sheet guide in the fourth embodiment. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       [0025]    In  FIG. 1 , a sheet tray  51  is disposed, and a sheet feeding part  30  is provided in a sheet feeding side of the sheet tray  51  in the lower part of an image forming apparatus  1  having a configuration as an electrographic printer. Recording sheets  52  are stacked in the sheet tray  51 , and the sheet feeding part  30  feeds the recording sheets  52  as a media one by one. A pickup roller  31 , a feed roller  32 , and a separation piece  33  are provided in the sheet feeding part  30 . The pickup roller  31  is provided so as to be contacted and pressed against the recording sheets  52  stacked to a certain height. The feed roller  32  and the separation piece  33  separate the recording sheets  52  fed by the pickup roller  31  one by one. 
         [0026]    A manual feed tray  300  is provided with a medium stacking device  302 , a pickup roller  303 , a feed roller  304  and a retard roller  305 . The recording sheets  370  ( FIG. 2 ) are stacked on the medium stacking device  302 . The pickup roller  303  is provided so as to be contacted and pressed against a contact part  311  ( FIG. 2 ) of a medium stacking plate  310  of the medium stacking device  302 . The feed roller  304  and the retard roller  305  separate the sheets one by one fed by the pickup roller  303 . The recording sheets  370  on the medium stacking device  302  are fed to the feed roller  304  by rotation of the pickup roller  303  by drive of motor (not shown), are separated one by one by the feed roller  304  and the retard roller  305 , and are sent to a sheet carrying part  40 . 
         [0027]    The sheet carrying part  40  carries each of the recording sheets  52  that are separated into a sheet and fed from the sheet feeding part  30  to an image forming part  10  via carrying roller pairs  41 ,  42 , and carries the recording sheets  370  ( FIG. 2 ) separated into a sheet and fed from the manual feed tray  300  via the carrying roller pair  42  to the image forming part  10  in the same manner. The image forming part  10  includes four toner image forming parts  11 K,  11 Y,  11 M,  11 C (if not necessary to be especially distinguished, may merely be referred to as a toner image forming part  11 ) sequentially and tandemly arranged from the upstream side of the carrying direction of the recording sheets  52 ,  370  and, a transfer part  13  transferring a toner image formed by the toner image forming part  11  on the upper surface of the sheet by Coulomb force. 
         [0028]    The toner image forming part  11 K forms a black (K) toner image. The toner image forming part  11 Y forms a yellow (Y) toner image. The toner image forming part  11 M forms a magenta (M) toner image. The toner image forming part  11 C forms a cyan (C) toner image. In each toner image forming part  11 , the photosensitive drum  12  is charged by a charging roller (not shown), image data is written on the rotating photosensitive drum  12  by a light head (not shown), and the image data is developed with toner. Thereby, each color of the toner images can be obtained on the photosensitive drum  12 . 
         [0029]    The transfer part  13  includes a transfer belt  14  carrying the recording sheet  52  carried from the sheet tray  51  or the recording sheet  370  ( FIG. 2 ) carried from the manual feed tray  300  in the arrow direction, and four transfer rollers  15  disposed so as to face each photosensitive drum  12  of each toner image forming part  11  across the transfer belt  14 . The transfer part  13  sequentially transfers the toner image to the recording sheet  52 , the toner image for each color being formed by Coulomb force on each photosensitive drum  12  corresponding to each toner image forming part  11 . 
         [0030]    A fuser  20  fixes the toner image transferred on the recording sheets  52 ,  370  in the transfer part  13  on the recording sheet by heat and pressure. The recording sheets  52 ,  370  on which the toner image is fixed are ejected on a stacking part  56  on which the printed recording sheets are stacked via a carrying roller pair  53  and an ejection roller pair  54 . 
         [0031]    Each of the axes of X, Y, and Z, in  FIG. 1  are as follows: X axis is the carrying direction when the recording sheet  52  passes the image forming part  10 ; Y axis is the rotation axial direction of the photosensitive drum  12 ; and Z axis is the direction orthogonal to the above mentioned axes. In addition, in a case where each of the axes of X, Y, and Z are shown in the other figures mentioned below, the rotation axial directions respectively indicates identical directions. That is, X, Y, and Z axes in each of the figures show disposition directions of description parts in each of figures configuring the image forming apparatus  1  shown in  FIG. 1 . Note that the image forming apparatus  1  is herein disposed so that Z axis is a substantially vertical direction. 
         [0032]      FIG. 2  is a configuration diagram viewed from the front surface (Y axis plus side) of a manual feed tray  300 .  FIG. 3  is an external perspective view illustrating the configuration of the medium stacking device  302 .  FIG. 4  is a configuration diagram viewed from the lower side of the medium stacking device  302 . 
         [0033]    In  FIG. 2 , a frame  301  of the manual feed tray  300  is fixed to the image forming apparatus  1  main body. The medium stacking device  302  stacking the recording sheets  370  is rotatably held by the frame  301  as mentioned below. Note that parts other than the manual feed tray  300  of the image forming apparatus  1  may referred to as the image forming apparatus  1  main body. The pickup roller  303  is dispose at a position so as to contact the contact part  311  of the medium stacking plate  310  of the medium stacking device  302 . The feed roller  304  is rotatably held by the image forming apparatus  1  main body, and is rotated and driven by a drive motor (not shown). An idler gear  306  links the pickup roller  304  to the feed roller  303 . The retard roller  305  is linked to a torque limiter (not shown). A spring  308  biases the retard roller  305  toward the feed roller  304 . A spring  309  biases the medium stacking device  302  toward a direction in which the contact part  311  of the medium stacking device  302  contact pickup roller  303 . 
         [0034]    Note that the manual feed tray  300  herein, for example, includes the frame  301 , the medium stacking device  302 , the pickup roller  303 , the spring  309 , and the idler gear  306 . 
         [0035]    As shown in  FIG. 3  and  FIG. 4 , the medium stacking device  302  includes the medium stacking plate  310  as a medium stacking part, a sheet guide  320  as a first movement part, a sheet guide  321  as a second movement part, a pinion gear  381  as a first gear part, and a pinion gear  382  as a second gear part. A pair of posts  335 ,  336  formed on both of end parts of the medium stacking plate  310  are respectively inserted into guide grooves  301   a ,  301   b  ( FIG. 2 ) formed on the frame  301 . Thereby, the medium stacking device  302  is rotatably held. Furthermore, as mentioned above, the contact part  311  of the medium stacking device  302  is biased in the direction where the contact part  311  contacts the pickup roller  303  by the spring  309 . The pinion gears  381  and  382  are positioned along in the medium carrying direction and at a substantially middle of the sheet guides  320  and  321 . 
         [0036]      FIG. 5  is an external perspective view illustrating a configuration of the surface (upper surface) of a medium stacking plate  310  of the medium stacking device  302 .  FIG. 6  is an external perspective view illustrating a configuration of the rear surface (lower surface) of the medium stacking plate  310 . 
         [0037]    As shown in  FIG. 5  and  FIG. 6 , a center plate part  340  is formed in a center part of the medium stacking plate  310 , and extends in a direction of arrow A (vertical to Y axis, however not always vertical to Z axis) indicating a carrying direction of the stacked recording sheets  370  ( FIG. 2 ). Guide grooves  331 ,  332 ,  333 ,  334  are alternately formed from both sides of the center plate part  340 . The guide grooves extend in a width direction (Y axis direction) of the stacked recording sheets. An insertion part  331   a ,  332   a ,  333   a ,  334   a  is formed in each guide groove  331 - 334 . The insertion parts  331  extend outward only a predetermined width in both directions which are orthogonal each other in a position close to the center plate part  340 . All of the guide grooves  331 - 334  and the insertion parts  331   a - 334   a  penetrate to the rear side of the medium stacking plate  310  as shown in  FIG. 6 . 
         [0038]      FIG. 7  is an external perspective view illustrating a configuration of a sheet guide  320  illustrated in  FIG. 3 . Note that since the configuration of the sheet guide  321  herein is identical to that of the sheet guide  320 , the configuration will be explained with reference to the sheet guide  320 . 
         [0039]    The sheet guide  320  includes a guide block  350  extending in the direction of arrow A along which the stacked recording sheets are carried, and a pair of racks  355 ,  356  as a first movement restriction part extending in the width direction (Y axis direction) of the recording sheet. A restriction surface  351  as a first medium restriction part and a stacking surface  352   a  are formed in the guide block  350 . The restriction surface  351  that is vertical surface with respect to Y axis, extends in the direction of arrow A, and restricts a position of the width direction of the recording sheet. The stacking surface  352   a  that is orthogonal to the restriction surface  351  extends in the direction of arrow A. The edges of the width direction of the recording sheets are stacked on the stacking surface  352   a . Note that a pair of racks  355 ,  356  of the sheet guide  321  corresponds to a second movement restriction part. The restriction surface  351  of the sheet guide  321  corresponds to a second medium restriction part. In this embodiment, each of the movement restriction parts is realized with two restriction members (racks  355  and  356 ). The number of the restriction members for one movement restriction part is preferably two, but may be three or more. 
         [0040]    Rack holding members  353 ,  354  respectively holding the racks  355 ,  356  are formed below a plate-shaped part  352 . The upper surface of the plate-shaped part  352  is the stacking surface  352   a . The each rack  355 ,  356  projects downward from the lower surface of the plate-shaped part  352  so that the upper surface of each rack  355 ,  356  and the lower surface of the plate-shaped part  352  have a predetermined interval g. As shown in  FIG. 7 , the racks  355 ,  356  have the predetermined interval between them, and are formed at a position where the racks shifted in the direction of arrow A with respect to a width center of the guide block  350 . The position relationship of these will be explained below. 
         [0041]    The rack  355  and the rack  356  are plate-shaped members having flat surfaces in parallel to the stacking surface  352   a . The racks  355  and the rack  356  are formed vertically with respect to the restriction surface  351 , and have a substantially identical shape, and are formed in parallel. A restriction part  355   b  and a restriction part  356   b  are formed in one edge of the guide block side of the rack  355  and the rack  356 . A restriction part  355   f  and a restriction part  356   f  are formed in the other edge of the guide block side of the rack  355  and the rack  356 . In addition, in the opposite side of arrow A of the rack  355  and the rack  356 , a tooth part  355   d  and a tooth part  356   d  are formed between both of the restriction parts, and in the arrow A side, a pair of bias parts  355   c ,  355   e  and a pair of bias parts  356   c ,  356   e  are formed in the neighborhood of both of the restriction parts. 
         [0042]    As shown in  FIG. 3  and  FIG. 4 , the rack holding members  353 ,  354  of the sheet guide  320  are installed to the medium stacking plate  310  so that the rack holding members  353 ,  354  are respectively guided to the guide grooves  333 ,  331  of the medium stacking plate  310 . The rack holding members  353 ,  354  of the sheet guide  321  are installed to the medium stacking plate  310  so that the rack holding members  353 ,  354  are respectively guided to the guide grooves  332 ,  334  of the medium stacking plate  310 . Installation method of the guide grooves will be explained hereinafter. 
         [0043]    Here, the case where the sheet guide  320  shown in  FIG. 7  is installed to the medium stacking plate  310  shown in  FIG. 5  and  FIG. 6  will be explained. First, the sheet guide  320  is rotated substantially 90 degrees around X axis in a direction of arrow B. Respectively, a front edge of the restriction part  355   f  of the rack  355  is inserted in a direction of arrow C ( FIG. 5 ) so that the front edge is substantially vertically inserted into the insertion part  333   a  of the guide groove  333  of the medium stacking plate  310 . In addition, a front edge of the restriction part  356   f  of the rack  356  is inserted in a direction of arrow C ( FIG. 5 ) so that the front edge is substantially vertically inserted into the insertion part  331   a  of the guide groove  331  of the medium stacking plate  310 . The sheet guide  320  is pushed and entered until the plate-shaped part  352  abuts on the upper surface of the medium stacking plate  310 . 
         [0044]    For this reason, the width of the insertion part  333   a  is made to be wider than each width Wa 1 , Wa 2  of the restriction parts  355   b ,  355   f . In addition, the width of the insertion part  333   a  is made to be wider than each width Wb 1 , Wb 2  of the restriction parts  356   b ,  356   f . Furthermore, the width of the rack holding part  353  is made to be narrower than each width Wa 1 , Wa 2  of the restriction parts  355   b ,  355   f . The width of the guide groove  333  is formed to have a width suitable for guiding the inserted rack holding member  353 . In the same manner, the width of the rack holding part  354  is made to be narrower than each width Wb 1 , Wb 2  of the restriction parts  356   b ,  356   f . The width of the guide groove  331  is formed to have a width suitable for guiding the inserted rack holding member  354 . 
         [0045]    At the stage where the plate-shaped part  352  abuts on the upper surface of the medium stacking plate  310 , the sheet guide  320  is rotated around X axis in the opposite direction of a direction of arrow B. Thereby, the rack holding member  353  and the rack holding member  354  is respectively inserted into to the guide groove  333  and the guide groove  331 , and the rack  355  and the rack  356  respectively extends in parallel via the medium stacking plate  310  on the lower surface of the medium stacking plate  310 . Furthermore, until the guide block  350  is positioned at one end side of the medium stacking plate  310 , the sheet guide  320  is guided and moved by the guide grooves  333 ,  331 . Thereby, the sheet guide  320 , for example, as shown in  FIG. 3 , is placed at an initial position. The initial position mentioned herein indicates a farthest part position of the sheet guide  321 . 
         [0046]    In the same manner, a front edge of the restriction part  355   f  of the rack  355  of the sheet guide  321  is inserted in a direction of arrow C ( FIG. 5 ) so that the front edge is substantially vertically inserted into the insertion part  332   a  of the guide groove  332  of the medium stacking plate  310 . In addition, a front edge of the restriction part  356   f  of the rack  356  is inserted in a direction of arrow C ( FIG. 5 ) so that the front edge is substantially vertically inserted into the insertion part  334   a  of the guide groove  334  of the medium stacking plate  310 . Until the guide block  350  is positioned at another end side of the medium stacking plate  310 , the sheet guide  321  is guided and moved by the guide grooves  332 ,  334 . Thereby, the sheet guide  321 , for example, as shown in  FIG. 3 , is placed at the initial position. 
         [0047]    As shown in  FIG. 4  and  FIG. 6 , the guide wall  341   a  and the guide wall  341   b  are formed on the lower surface of the medium stacking plate  310 . The guide wall  341   a  faces the bias parts  356   c ,  356   e  of the rack  356  of the sheet guide  320 . The guide wall  341   b  faces the abutment parts  356   a ,  356   g  of the rack  356  of the sheet guide  320 . The abutment parts  356   a ,  356   g  receive bias force from the bias parts  356   c ,  356   e , contact the guide wall  341   b , and guide the movement of the rack  356  of the sheet guide  320  without shaking the sheet guide. In the same manner, the guide wall  342   a  and the guide wall  342   b  are formed on the lower surface of the medium stacking plate  310 . The guide wall  342   a  faces the bias parts  355   c ,  355   e  of the rack  355  of the sheet guide  320 . The guide wall  342   b  faces the abutment parts  355   a ,  355   g  of the rack  355  of the sheet guide  320 . The abutment parts  355   a ,  355   g  receive bias force from the bias parts  355   c ,  355   e , contact the guide wall  342   b , and guide the movement of the rack  355  of the sheet guide  320  without shaking the sheet guide. The guide walls  341   a  and  341   b  functions as support parts for the abutment parts  356   a  and  356   g . The support parts function to allow the first and second medium restriction parts to move in predetermined directions. In the embodiments, the abutment parts  355   a ,  355   g  of the rack  355  contact the guide walls  341   a ,  341   b , and slidably move along the surfaces of the guide walls  341   a ,  341   b . As long as the support parts allows the medium restriction parts to move without shaking the sheet guide, there is no structural or material restriction for the support parts. For example, the support part may have a curved surface other than the plane surface. The support part may have a projection shape which protrudes toward the abutment part and of which a tip contacts the abutment part so that the movement of the abutment part is restricted by the tip of the support part. 
         [0048]    In the same manner, the guide wall  344   a  and the guide wall  344   b  are formed on the lower surface of the medium stacking plate  310 . The guide wall  344   a  faces the bias parts  356   c ,  356   e  of the rack  356  of the sheet guide  321 . The guide wall  344   b  faces the abutment parts  356   a ,  356   g  of the rack  356  of the sheet guide  321 . The abutment parts  356   a ,  356   g  receive bias force from the bias parts  356   c ,  356   e , contact the guide wall  344   b , and guide the movement of the rack  356  of the sheet guide  321  without shaking the sheet guide. In the same manner, the guide wall  343   a  and the guide wall  343   b  are formed on the lower surface of the medium stacking plate  310 . The guide wall  343   a  faces the bias parts  355   c ,  355   e  of the rack  355  of the sheet guide  321 . The guide wall  343   b  faces the abutment parts  355   a ,  355   g  of the rack  355  of the sheet guide  321 . The abutment parts  355   a ,  355   g  receive bias force from the bias parts  355   c ,  355   e , contact the guide wall  343   b , and guide the movement of the rack  355  of the sheet guide  321  without shaking the sheet guide. 
         [0049]      FIG. 8  is a diagram excluding the medium stacking plate  310  from the configuration diagram of  FIG. 4  in the first embodiment.  FIG. 9  is a K-K cross-sectional view illustrating a cross-section along a position passing a center of screws  345 ,  346  illustrated in  FIG. 4 . 
         [0050]    As shown in  FIG. 8 , the sheet guide  320  and the sheet guide  321  have a substantially identical shape. When the sheet guides are installed to the medium stacking plate  310  and each the sheet guide is at the initial position, in the direction of arrow A that is the moving direction of the recording sheet, the racks  355 ,  356  of each sheet guide alternately are disposed in parallel at a predetermined interval. Especially, the tooth part  355   d  of the sheet guide  320  is adjacent to the tooth part  356   d  of the sheet guide  321  and the tooth part  356   d  of the sheet guide  320  is adjacent to the tooth part  355   d  of the sheet guide  321 . One part of a region of each of front edge sides of the tooth parts adjacent to each other face at a predetermined interval in the center part of the width direction (Y axis direction) of the recording sheet  370  of the medium stacking plate  310 . 
         [0051]    As shown in  FIG. 8 , the pinion gear  381  and the pinion gear  382  are respectively disposed in the center part of the width direction of the recording sheet  370  of the medium stacking plate  310  at a position where the tooth part  356   d  of the sheet guide  320  and the tooth part  355   d  of the sheet guide  321  face, and a position where the tooth part  355   d  of the sheet guide  320  and the tooth part  356   d  of the sheet guide  321  face. The pinion gear  381  and the pinion gear  382  are respectively rotatably fixed at the medium stacking plate  310  by the screw  345  and the screw  346 . 
         [0052]    As shown in  FIG. 9 , the tooth part  381   a  and a flange part  381   b  are formed in the pinion gear  381 . The tooth part  381   a  meshes with the tooth part  356   d  of the rack  356  of the sheet guide  320  and with the tooth part  355   d  of the rack  355  of the sheet guide  321 . The flange part  381   b  projects so as to cover each part of the rack  356  of the sheet guide  320  and the rack  355  of the sheet guide  321 . In the same manner, the tooth part  382   a  and a flange part  382   b  are formed in the pinion gear  382 . The tooth part  382   a  meshes with the tooth part  356   d  of the rack  356  of the sheet guide  321  and with the tooth part  355   d  of the rack  355  of the sheet guide  320 . The flange part  382   b  projects so as to cover each part of the rack  356  of the sheet guide  321  and the rack  355  of the sheet guide  320 . Note that, in  FIGS. 4 ,  8 , only each pitch circle (standard circle)  381   p ,  382   p  of each tooth part  381   a ,  382   a  of the pinion gear  381 ,  382  are shown by dotted lines. 
         [0053]    The plate-shaped part  352  of the guide block  350  of the sheet guide  320  installed to the medium stacking plate  310  is restricted by the medium stacking plate  310 . In addition, the racks  355 ,  356  of the sheet guide  320  are restricted by each of the flange parts  381   b ,  382   b  of the pinion gears  381 ,  382 . Accordingly, the sheet guide  320  is not detached below (here, the minus side of Z axis). In addition, since the widths of the racks  355 ,  356  are respectively formed wider than the widths of the guide grooves  331 ,  333  of the medium stacking plate  310 . Accordingly, the sheet guide  320  is not detached above (here, plus side of Z axis). In the same manner, the sheet guide  321  installed to the medium stacking plate  310  is configured so as not to detach in upper and lower directions with respect to the medium stacking plate  310 . 
         [0054]    Note that, as shown in  FIG. 9 , a wave washer  383  is arranged in a compressed manner between the pinion gear  382  and the medium stacking plate  310 , and biases the pinion gear  382  toward the screw  346 . This wave washer  383  adjusts a rotation load of the pinion gear  382 , and thereby, adjusts the movement load of the sheet guides  320 ,  321 . The wave washer  383  may respectively be provided to the two pinion gears  381 ,  382 . However, here, as described below since two of the pinion gears  381  and  382  link each other, the wave washer  383  may provided only to the pinion gear  382 . 
         [0055]    As shown in  FIG. 4  (see  FIG. 8 ), the abutment parts  356   a ,  356   g  of the sheet guide  320  contact the guide wall  341   b  of the medium stacking plate  310  by bias from the bias parts  356   c ,  356   e , and restrict an mesh position of the pinion gear  381  and the rack  356  as well as a movement range of the sheet guide  320  with respect to the medium stacking plate  310 . In the same manner, the abutment parts  355   a ,  355   g  of the sheet guide  320  contact the guide wall  342   b  of the medium stacking plate  310  by bias from the bias parts  355   c ,  355   e , and restrict an mesh position of the pinion gear  382  and the rack  355  as well as a movement range of the sheet guide  320  against the medium stacking plate  310 . 
         [0056]    Meanwhile, the abutment parts  356   a ,  356   g  of the sheet guide  321  contact the guide wall  344   b  of the medium stacking plate  310  by bias from the bias parts  356   c ,  356   e , and restrict an mesh position of the pinion gear  382  and the rack  356  as well as a movement range of the sheet guide  321  with respect to the medium stacking plate  310 . In the same manner, the abutment parts  355   a ,  355   g  of the sheet guide  321  contact the guide wall  343   b  of the medium stacking plate  310  by bias from the bias parts  355   c ,  355   e , and restrict an mesh position of the pinion gear  381  and the rack  355  as well as a movement range of the sheet guide  321  against the medium stacking plate  310 . 
         [0057]      FIG. 10  is a size explanation diagram illustrating a position relationship between the sheet guides  320 ,  321  installed to the medium stacking plate  310  and the pinion gears  381 ,  382  rotatably axially fixed to the medium stacking plate  310 . Note that, here, for the sake of convenience, “′” are putted to the reference numbers of each configuration element of the sheet guide  321 , to distinguish each configuration element of the sheet guide  320 . Note that  FIG. 10  corresponds to  FIG. 8  the medium stacking device  302  viewed from the lower side (the minus side of Z axis), and the direction of arrow A in  FIG. 10  shows the carrying direction of the stacked recording sheet. 
         [0058]    As shown in the above figure, the sheet guides  320 ,  321  have the same identical figure. Restriction surfaces  351 ,  351 ′ face each other and extend in the direction of arrow A. And the racks  355 ,  356  of the sheet guide  320  and the racks  355 ′,  356 ′ of the sheet guide  321  are disposed so as to be alternately positioned in the direction of arrow A. Furthermore, the pinion gear  381  is disposed so as to mesh with each of the racks between the rack  356  of the sheet guide  320  and the rack  355 ′ of the sheet guide  321  extending each other in parallel. The pinion gear  382  is disposed so as to mesh with each of the racks between the rack  355  of the sheet guide  320  and the rack  356 ′ of the sheet guide  321 . 
         [0059]    A length in the direction of arrow A of the guide block  350  ( 350 ′) is defined as L. A diameter of each pitch circle (standard circle)  381   p ,  382   p  of each pinion gear  381 ,  382  disposed in line in direction of arrow A is defined as d. A position relationship between the rack  355  ( 355 ′) and the rack  356  ( 356 ′) extending in parallel to the rack  355  will be explained. 
         [0060]    A hypothetical center line being the perpendicular bisector between each of rotation centers  381   c ,  382   c  of the pinion gears  381 ,  382  and extending in a width direction (Y axis direction) of the stacked recording sheet is defined as P. A distance from the hypothetical center line P to the rotation center  381   c  is defined as X. A distance from the hypothetical center line P to the rotation center  382   c  is defined as X. 
         [0061]    At this time, a distance from the hypothetical center line P to a pitch line (standard line)  355   p ′ of the rack  355 ′ being an engagement position of the pinion gear  381  is defined as Z. The distance Z is obtained by the following Formula: 
         [0000]        Z=X−d/ 2. 
         [0000]    The tooth part  355   d  ( FIG. 8 ) is formed so that this position is a pitch line (standard line)  355   p ′ of the rack  355 ′. In addition, a distance from the pitch line (standard line)  355   p ′ of the rack  355 ′ to a pitch line (standard line)  356   p ′ of the rack  356 ′ being the engagement position with the pinion gear  382  is defined as Y. The distance Y is obtained by the following Formula: 
         [0000]        Y= 2 X.    
         [0000]    The tooth part  356   d  ( FIG. 8 ) is formed so that this position is a pitch line (standard line)  356   p ′ of the rack  356 ′. 
         [0062]    In addition, with respect to the restriction surface  351 ′ having the length L in the direction of arrow A, the substantially center in the direction of arrow A of the restriction surface  351 ′ is disposed so as to coincide with the hypothetical central line P, and at least one of the racks  355 ′,  356 ′ is disposed in the direction of arrow A side (downstream side) and the opposite side of the direction of arrow A side (upstream side) based on the substantially center. Note that, in the drawing, rack  355 ′ on the downstream side, rack  356 ′ on the upstream side. In this case, obviously shown in the arrangement in  FIG. 10 , when a width of the rack  355 ′ is defined as w 1 , and a width of the rack  356 ′ is defined as w 2 , Z and K are necessary to be set by the following formulae: 
         [0000]        Z&gt;w 1, and 
         [0000]        K=L/ 2−( Z+d )&gt; w 2.
 
         [0063]    By forming in this manner, the sheet guide  320  and the sheet guide  321  having the same shape can be disposed and face each other, can be installed to the medium stacking plate  310 . 
         [0064]    Note that, here, the substantially center in the direction of arrow A of the restriction surface  351 ′ is disposed so as to coincide with the hypothetical central line P. However, if the substantially center mentioned herein indicates the hypothetical center line P being included in a region having a length of L/2±20%, same effects can be obtained by the arrangement of the line P. 
         [0065]    In addition, the engagement position mentioned herein is a position where the pinion gear  381  meshes with the racks  355 ′,  356 , and the pinion gear  382  meshes with the racks  355 ,  356 ′.  FIGS. 11A and 11B  are partially enlarged diagrams for explaining an engagement position with a mesh of the pinion gear  381  and the rack  355 ′ as an example. 
         [0066]    As shown in  FIG. 11A , the pinion gear  381  and the rack  355 ′ are engaged so that one of tangential lines of the pitch circle (standard circle)  381   p  of the pinion gear  381  is positioned in the substantially center of a range h 2  from an addendum to a dedendum of the tooth part  355   d ′ of the rack  355 ′. A position on the rack  355 ′ where the pitch circle (standard circle)  381   p  of the pinion gear  381  contacts in this way corresponds to the pitch line (standard line)  355   p ′ of the rack. Accordingly, the engagement position mentioned herein corresponds to a position where the pitch circle (standard circle) of the pinion gear contacts the pitch line (standard line) of the rack. 
         [0067]    The above mentioned engagement position is merely one example. The engagement position may be a position in a region where a range h 1  and the range h 2  intersect. The range h 1  is from the addendum to the dedendum of the tooth part  381   a  of the pinion gear  381 . The range h 2  is from the addendum to the dedendum of the tooth part  355   d ′ of the rack  355 ′. For example, as shown in  FIG. 11B , in a case where the pinion gear  381  is shifted, a position relationship causing the pinion gear  325  to engage with the rack  355 ′ differs from that shown in  FIG. 11A . The engagement position of the other pinion gear with the rack is identical to the above mentioned engagement position. 
         [0068]    In addition, for example, the tooth part  355   d  of the rack  355  and the tooth part  356   d  of the rack  356  have the identical pitch and the identical phase viewed from the restriction surface  351  in the sheet guide  320  shown in  FIG. 7 . The sheet guide  321  is configured in the same manner as mentioned above. In addition, for example, the pinion gear  381  and the pinion gear  382  shown in  FIG. 8 , have the identical number of teeth, and as shown in  FIG. 11 , the number herein is 16, which is even number. Furthermore, the pinion gears respectively include the flange parts  381   b ,  382   b , and have the identical module. 
         [0069]    In the above mentioned configuration, operation of the sheet guides  320 ,  321  in the medium stacking device  302  of the manual feed tray  300  will be explained with reference to  FIG. 12 . Note that  FIG. 12  is a diagram used to an operation explanation of the sheet guides  320 ,  321  of the medium stacking device  302  stacking recording sheets  370 . In the above figure, only a region in the recording sheet  370  where the medium stacking device exists is specified by drawing with diagonal lines. 
         [0070]    Firstly, the medium stacking device  302  is pushed down against bias of the spring  309  by an operation device (not shown), so that the contact part  311  of the medium stacking device  302  shown in  FIG. 2  is separated only at a predetermined interval from the pickup roller  303 , and the medium stacking device  302  is restricted at the position where the medium stacking device  302  is pushed down. In the state where the medium stacking device  302  is pushed down in this way, the recording sheets  370  are placed on the manual feed tray  300 . At this time, the sheet guide  320  and the sheet guide  321  are moved to outside and the recording sheets  370  are stacked on the medium stacking device  302  so that the width direction edges of the recording sheet  370  are positioned on each of the stacking surfaces  352   a  of the sheet guide  320  and the sheet guide  321 . Each of the restriction surfaces  351  of the sheet guides  320  and  321  are moved in a center direction until the restriction surfaces  351  abut on end surfaces of the recording sheets  370 . 
         [0071]    At this time, each of the restriction surfaces  351  of the sheet guide  320  and the sheet guide  321  are symmetrically moved away from and toward a line connecting each of the rotate center s of the pinion gears  381  and  382  (see  FIG. 8 ) as the center line. Accordingly, when the guide block  350  of either the sheet guide  320  or sheet guide  321  is moved, the other guide block  350  is also symmetrically moved via the pinion gears. Thereby, the width direction position of the recording sheet  370  can be restricted. 
         [0072]    As mentioned above, since the tooth part  355   d  of the rack  355  and the tooth part  356   d  of the rack  356  are configured to have the identical pitch and the identical phase viewed from the restriction surface  351 , and the pinion gear  381  and the pinion gear  382  have the identical shape, even if a rack and pinion is configured with the two racks  355 ,  356  in this way, sliding motion can be smoothly performed. 
         [0073]    After determination of a position of the width direction of the recording sheet  370  on the medium stacking device  302  is performed as mentioned above, position restriction by an operation device (not shown) is unlocked, and as shown in  FIG. 2 , the top sheet of the stacked recording sheets  370  contacts the pickup roller  303  by bias force of the spring  309 . In such a state, the pickup roller  303  activates and the recording sheet  370  is fed, the recording sheet  370  is fed in the direction of arrow A in  FIG. 12 . At this time, the recording sheet  370  may skew in a rotation direction of either arrow Ma or arrow Mb. 
         [0074]    For example, when the recording sheet  370  skews in the direction of arrow Ma, the rear edge side in the direction of arrow A of the restriction surface  351  of the sheet guide  321  receives a pressure force Fa from the recording sheet  370  generated by skew, and the front edge side in the direction of arrow A of the restriction surface  351  of the sheet guide  320  receives a pressure force Fc from the recording sheet  370  generated by skew. At this time, a movement force Fd is generated at the front edge side of the sheet guide  321  toward the center direction to rotate in the direction of arrow Mc, a movement force Fb is generated at the rear edge side of the sheet guide  320  toward the center direction to rotate in the direction of arrow Md. 
         [0075]    At this time, the movement force Fd, which is generated at the front edge side of the sheet guide  321 , is led to the front edge side of the sheet guide  320  via the rack  355 ′ of the sheet guide  321 , the pinion gear  381 , the rack  356  of the sheet guide  320  shown in  FIG. 10 , and reaches the front edge side of the sheet guide  320  as a force cancelling the pressure force Fc from the recording sheet  370 . In the same manner, the movement force Fb, which is generated at the rear edge side of the sheet guide  320 , is led to the rear edge side of the sheet guide  321  via the rack  355  of the sheet guide  320 , the pinion gear  382 , the rack  356 ′ of the sheet guide  321  shown in  FIG. 10 , and reaches the rear edge side of the sheet guide  320  as a force cancelling the pressure force Fa from the recording sheet  370 . 
         [0076]    In a case where the recording sheet  370  skews in the direction of arrow Mb, in the same manner, a pressure force which each sheet guide  320 ,  321  respectively receives from the recording sheet  370  is cancelled. 
         [0077]    As mentioned above, according to the medium stacking device of the embodiment, since the pinion gears  381 ,  382  arranged at the positions being separated in the direction of arrow A respectively link to the racks extending from the sheet guides  320 ,  321 , even if skew is generated in the carried recording sheet, an incline of the sheet guides  320 ,  321  is suppressed, and the skew of the recording sheet can be diminished. 
       Second Embodiment 
       [0078]      FIG. 13  is a configuration diagram viewed from the lower side (the minus side of Z axis) of the medium stacking device  402  in the second embodiment according to the present invention.  FIG. 14  is an M-M cross-sectional view illustrating a cross-section along a position passing a center of screws  345 ,  346  shown in  FIG. 13 . The upper side of the medium stacking device  402  is placed up in  FIG. 4 . 
         [0079]    The image forming apparatus employing this medium stacking device  402  has main different points from the image forming apparatus employing the above mentioned medium stacking device  302  of the first embodiment shown in  FIG. 4 . The points are that, for example, upper layer gears  481   d ,  482   d  are added to the pinion gears  481 ,  482  ( 381 ,  382  in embodiment 1) and the pinion gears are formed as a two stage gear, and that an idler gear  400  meshing with these upper gears  481   d ,  482   d  is added. In the invention, a transferring part means a part that functions to convey a power from the first gear part to the second gear part. In this embodiment, the transferring part is configured with the upper layer gears  481   d ,  482   d  and idler gear  400 . As long as the transferring part is able to convey the power from the first gear part to the second gear part, there is no structural restriction. The number of parts, gears for the transferring part vary according to the configuration. Instead of the mechanical structure by gears discussed above, friction force or magnetic force may be useful to realized the transferring part. 
         [0080]    Accordingly, the same reference numbers are put to, and explanation and figures are omitted for parts of the image forming apparatus employing this medium stacking device  402  that are common with the image forming apparatus  1  of the first embodiment mentioned above ( FIG. 1 ). Different parts of the image forming apparatus from those of the image forming apparatus  1  are intensively explained. Note that since the main configuration of the image forming apparatus of the embodiment is common with the main configuration of the image forming apparatus  1  of the first embodiment shown in  FIG. 1  other than the medium stacking device  402 ,  FIGS. 1 ,  2  will be referred if needed. 
         [0081]    In  FIG. 13  and  FIG. 14 , in the pinion gears  481 ,  482 , not only the first stage gear meshing with each rack, as explained in the first embodiment, but also the upper layer gears  481   d ,  482   d  being a second stage gear are formed via flange parts  481   b ,  482   b . In  FIG. 13 , pitch circles of the upper layer gears  481   d ,  482   d  are shown. The idler gear  400  is disposed in the center part of these pinion gears  481 , 482 , and is rotatably fixed in the center point between axes of the pinion gears  481 ,  482  by a screw  401  to medium stacking plate  310 . In  FIG. 13 , a pitch circle  400   p  of the idler gear  400  is shown by dotted lines. 
         [0082]    As shown in  FIG. 14 , a wave washer  405  is arranged in a compressed manner between the idler gear  400  and the medium stacking plate  310  and, biases the idler gear  400  toward the screw  401 . Note that a notch part  455   h  for allowing attachment of the idler gear  400  to the medium stacking plate  310  is formed in a rack  455  ( 355  in the first embodiment) of the sheet guides  420 ,  421  ( 320 ,  321  the first embodiment). 
         [0083]    The idler gear  400  respectively meshes with each upper layer gear  481   d ,  482   d  of these pinion gears  481 ,  482  at the center parts of the pinion gears  481 ,  482  and causes the pinion gear  481  to link to the pinion gear  482 . 
         [0084]    Note that, here, the sheet guide  420  corresponds to a first movement part. The sheet guide  421  corresponds to a second movement part. The pair of racks  455 ,  456  of the sheet guide  420  corresponds to a first movement restriction part. The pair of racks  455 ,  456  of the sheet guide  421  corresponds to a second movement restriction part. The restriction surface  351  of the sheet guide  420  corresponds to a first medium restriction part. The restriction surface  351  of the sheet guide  421  corresponds to a second medium restriction part. 
         [0085]    In the above mentioned configuration, operation of the sheet guide  420 ,  421  in the medium stacking device  402  of will be explained with reference to  FIG. 15 . Note that  FIG. 15  is a diagram used to an operation explanation of the sheet guides  420 , 421  of the medium stacking device  402  stacking the recording sheets  370 . In the above figure, only a region in the recording sheet  370  where the medium stacking device exists is specified by drawing with diagonal lines. 
         [0086]    Firstly, the medium stacking device  402  is pushed down against bias of the spring  309  by an operation device (not shown), so that the contact part  311  of the medium stacking device  302  shown in  FIG. 2  (herein referred to as  402 ) is separated only at a predetermined interval from the pickup roller  303 , and the medium stacking device  402  is restricted at the position where the medium stacking device  402  is pushed down. In the state where the medium stacking device  402  is pushed down in this way, the recording sheets  370  are placed on the manual feed tray  300 . At this time, the sheet guide  420  and the sheet guide  421  are moved to outside and the recording sheets  370  are stacked on the medium stacking device  402  so that the width direction edges of the recording sheet  370  are positioned on each of the stacking surfaces  352   a  of the sheet guide  420  and the sheet guide  421 . Each of the restriction surfaces  351  of the sheet guides  420  and  421  are moved in a center direction until the restriction surfaces  351  abut on end surfaces of the recording sheets  370 . 
         [0087]    At this time, each of the restriction surfaces  351  of the sheet guide  420  and the sheet guide  421  are symmetrically moved away from and toward and a line connecting each of the rotate centers of the pinion gears  481  and  482  (see  FIG. 13 ) as the center line. At this time, the pinion gear  481  and the pinion gear  482  simultaneously rotate in the identical direction with the movement of the sheet guide  420  and the sheet guide  421 , while the idler gear  400  links these gears rotating in the opposite direction. As mentioned above, in the case where the idler gear  400  is added, even the two racks  455 , 456  are used to configure the rack and pinion, sliding motion can be smoothly performed. 
         [0088]    Thereby, after determination of a position of the width direction of the recording sheet  370  on the medium stacking device  402  is performed as mentioned above, position restriction by an operation device (not shown) is unlocked and as shown in  FIG. 2 , the top sheet of the stacked recording sheets  370  contacts the pickup roller  303  by bias force of the spring  309 . In such a state, the pickup roller  303  activates and the recording sheet  370  is fed, the recording sheet  370  is fed in the direction of arrow A in  FIG. 15 . At this time, the recording sheet  370  may skew in a rotation direction of either arrow Ma or arrow Mb. 
         [0089]    For example, when the recording sheet  370  skews in the direction of arrow Ma, the rear edge side in the direction of arrow A of the restriction surface  351  of the sheet guide  421  receives the pressure force Fa from the recording sheet  370  generated by skew. At this time, the front edge side of the sheet guide  420  generates the movement force Fd toward the center direction to rotate in the direction of arrow Mc. 
         [0090]    These forces generated by skew toward the direction of arrow Ma cause the pinion gear  481  and the pinion gear  482  ( FIG. 13 ) to rotate in the opposite direction each other. However, these pinion gear  481  and pinion gear  482  linked by the idler gear  400  cannot rotate in the opposite direction each other. Accordingly, the sheet guide  421  does not rotate in the direction of arrow Ma. In the same manner, in a case where the recording sheet  370  skews toward the direction of arrow Mb, the sheet guide  421  does not rotate in direction of arrow Mb. Since the forces act with respect to the sheet guide  420  in the same manner, the sheet guide  420  and the sheet guide  421  can always keep the respective restriction surfaces  351  in parallel with respect to the direction of arrow A being the sheet carrying direction. 
         [0091]    As mentioned above, according to the medium stacking device of the embodiment, since the pinion gears  481 ,  482  arranged at the positions being separated in the direction of arrow A link to the idler gear  400 , even if skew is generated in the carried recording sheet, thereby, since an incline of the sheet guides  420 ,  421  is suppressed, and the skew of the recording sheet can be diminished. 
       Third Embodiment 
       [0092]      FIG. 16  is a configuration diagram of the medium stacking device  502  viewed from the lower side (the minus side of Z axis) in the third embodiment according to the present invention.  FIG. 17  is an external perspective view illustrating a configuration of a sheet guide  520  ( 521 ). 
         [0093]    The image forming apparatus employing this medium stacking device  502  has a main different point from the image forming apparatus employing the above mentioned medium stacking device  302  of the first embodiment shown in  FIG. 4 . The point is that instead of the pinion gears  381 ,  382 , the flanges  581 ,  582  without a gear are fixed by the screws  345 ,  346  to the medium stacking plate  310 , and plate-shaped extending parts  555 ,  556  are formed instead of the racks in each sheet guide  520 ,  521 . In this embodiment, the movement restriction parts are realized with two restriction members (extending parts  555  and  556 ). The number of the restriction members for one movement restriction part is preferably two, but may be three or more. 
         [0094]    Accordingly, the same reference numbers are put to, and explanation and figures are omitted for parts of the image forming apparatus employing this medium stacking device  502  that are common with the image forming apparatus  1  of the first embodiment mentioned above ( FIG. 1 ). Different parts of the image forming apparatus from those of the image forming apparatus  1  are intensively explained. Note that since the main configuration of the image forming apparatus of the embodiment is common with the main configuration of the image forming apparatus  1  of the first embodiment shown in  FIG. 1  other than the medium stacking device  502 ,  FIGS. 1 ,  2  will be referred if needed. 
         [0095]    The extending part  555  of the sheet guide  520  is formed to have a width forming a necessary minimum gap to guide and smoothly slide a side part  555   b  and a side part  555   a . The side part  555   b  is guided by the guide wall  342   a  formed in the medium stack plate  310  and the side part  555   a  is guided by the guide wall  342   b  formed in the medium stack plate  310 . In the same manner, the extending part  556  of the sheet guide  520  is formed to have a width forming a necessary minimum gap to guide and smoothly slide a side part  556   b  and a side part  556   a . The side part  556   b  is guided by the guide wall  341   a  formed in the medium stack plate  310  and the side part  556   a  is guided by the guide wall  341   b  formed in the medium stack plate  310 . 
         [0096]    Note that, here, the side parts  555   a ,  555   b  of the extending part  555  and the side parts  556   a ,  556   b  of the extending part  556  correspond to an abutment part. The guide walls  341   a ,  341   b ,  342   a , and  342   b  correspond to support parts. 
         [0097]    In addition, the extending part  555  of the sheet guide  521  is formed to have a width forming a necessary minimum gap to guide and smoothly slide a side part  555   b  and a side part  555   a . The side part  555   b  is guided by the guide wall  342   a  formed in the medium stack plate  310  and the side part  555   a  is guided by the guide wall  343   b  formed in the medium stack plate  310 . In the same manner, the extending part  556  of the sheet guide  521  is formed to have a width forming a necessary minimum gap to guide and smoothly slide a side part  556   b  and a side part  556   a . The side part  556   b  is guided by the guide wall  344   a  formed in the medium stack plate  310  and the side part  556   a  is guided by the guide wall  344   b  formed in the medium stack plate  310 . 
         [0098]    The flange  581  restricts detachment of the extending part  556  of the sheet guide  520  and the extending part  555  of the sheet guide  521  below (here, the minus side of Z axis. The flange  582  restricts detachment of the extending part  555  of the sheet guide  520  and the extending part  556  of the sheet guide  521  below (here, the minus side of Z axis). Accordingly, the respective sheet guide  520  and the sheet guide  521  herein individually move without linking each other. 
         [0099]    Note that, here, the sheet guide  520  corresponds to a first movement part. The sheet guide  521  corresponds to a second movement part. The pair of extending parts  555 ,  556  of the sheet guide  520  corresponds to a first movement restriction part. The pair of racks  555 ,  556  of the sheet guide  521  corresponds to a second movement restriction part. The restriction surface  351  of the sheet guide  520  corresponds to a first medium restriction part. The restriction surface  351  of the sheet guide  521  corresponds to a second medium restriction part. 
         [0100]    In the above mentioned configuration, operation of the sheet guides  520 ,  521  in the medium stacking device  502  will be explained. 
         [0101]    Firstly, the medium stacking device  502  is pushed down against bias of the spring  309  by an operation device (not shown), so that the contact part  311  of the medium stacking device  302  shown in  FIG. 2  (herein referred to as  502 ) is separated only at a predetermined interval from the pickup roller  303 , and the medium stacking device  502  is restricted at the position where the medium stacking device  502  is pushed down. In the state where the medium stacking device  502  is pushed down in this way, the recording sheets  370  are placed on the manual feed tray. At this time, the sheet guide  520  and the sheet guide  521  are moved to outside and the recording sheets  370  are stacked on the medium stacking device  502  so that the width direction edges of the recording sheet  370  are positioned on each of the stacking surfaces  352   a  of the sheet guide  520  and the sheet guide  521 . Each of the restriction surfaces  351  of the sheet guides  520  and  521  are moved in a center direction until the restriction surfaces  351  abut on end surfaces of the recording sheets  370 . 
         [0102]    At this time, since the sheet guide  520  and the sheet guide  521  do not link each other, they need to be individually moved by a user. 
         [0103]    After determination of a position of the width direction of the recording sheet  370  on the medium stacking device  502  is performed as mentioned above, position restriction by an operation device (not shown) is unlocked and as shown in  FIG. 2 , the top sheet of the stacked recording sheets  370  contacts the pickup roller  303  by bias force of the spring  309 . In such a state, the pickup roller  303  activates and the recording sheet  370  is fed, the recording sheet  370  is fed in the direction of arrow A in  FIG. 12 . 
         [0104]    At this time, in the case where skew generates in the recording sheet  370  and a pressure force acts on the restriction surface  351 , since a farthest side part of an extending part from a point of action of force contacts the guide wall of the medium stacking plate  310 , skew can be reduced in comparison with the case where only one extending part having similar dimension accuracy is used. 
         [0105]    For example, in the case where the sheet leading side (direction of arrow A side) of the restriction surface  351  of the sheet guide  520  shown in  FIG. 17  is pressed by a pressure force Fc 1  due to skew of the recording sheet stacked on the medium stacking device  502 , a front edge  555   h  of the side part  555   b  of the extending part  555  contacts the guide wall  342   a  ( FIG. 16 ) of the medium stacking plate  310 , thereby, an incline of the sheet guide  520  with respect to the direction of arrow A can be restricted. 
         [0106]    In the same manner, in the case where the sheet trailing side (opposite side of direction of arrow A side) of the restriction surface  351  of the sheet guide  520  shown in  FIG. 17  is pressed by a pressure force Fc 2  due to skew of the recording sheet stacked on the medium stacking device  502 , a front edge  556   h  of the side part  556   a  of the extending part  556  contacts the guide wall  341   b  ( FIG. 16 ) of the medium stacking plate  310 , thereby, an incline of the sheet guide  520  with respect to the direction of arrow A can be restricted. Such a mechanism of prevention of rotation of the sheet guide  521  disposed so as to face the sheet guide  520  is similar to the above mentioned mechanism. 
         [0107]    As mentioned above, according to the medium stacking device of the embodiment, even if skew is generated in the carried recording sheet, thereby, since an incline of the sheet guides  520 ,  521  is suppressed with respect to the sheet carrying direction (the direction of arrow A), and the skew of the recording sheet can be diminished. Furthermore, according to the explanation on  FIG. 10  of the first embodiment mentioned above, respectively, one of the extending part  556  and the extending part  555  is disposed in the direction of arrow A side and the other is disposed in the opposite side of the direction of arrow A side based on the center in the direction of arrow A of the restriction surface  351 . Thereby, the above mentioned effects of the embodiment can be more efficiently obtained regardless of directions of skew. 
         [0108]    Note, in the embodiment, the sheet guide to which the two extending parts are provided is shown as an example. However, same effects can be obtained by a sheet guide having two or more extending parts. 
       Fourth Embodiment 
       [0109]      FIG. 18  is an external perspective view illustrating a configuration of a sheet guide  620  ( 621 ) in the fourth embodiment. 
         [0110]    A medium stacking device employing the sheet guide  620  ( 621 ) has a main different point from the image forming apparatus employing the above mentioned medium stacking device  502  of third embodiment shown in  FIG. 16 . The point is that extending parts  655 ,  656  ( 555 ,  556  in the third embodiment) have a different shape from that of the extending parts  555 ,  556 . Accordingly, the same reference numbers are put to, and explanation and figures are omitted for parts of the image forming apparatus employing these sheet guides  620  ( 621 ) that are common with the image forming apparatus  1  of the first embodiment mentioned above ( FIG. 1 ). Different parts of the image forming apparatus from those of the image forming apparatus  1  are intensively explained. Note that since the main configuration of the image forming apparatus of the embodiment is common with the main configuration of image forming apparatus  1  of the first embodiment shown in  FIG. 1  other than the medium stacking device,  FIGS. 1 ,  2  will be referred if needed. In this embodiment, the movement restriction parts are realized with two restriction members (extending parts  655  and  656 ). The number of the restriction members for one movement restriction part is preferably two, but may be three or more. 
         [0111]    A shape of the extending part  655 ,  656  of the sheet guide  620  ( 621 ) corresponds to a shape of the rack  355 ,  356  of the sheet guide  320  ( 321 ) shown in  FIG. 7  explained in first embodiment other than the tooth parts  355   d ,  356   d . Accordingly, when this sheet guide  620  ( 621 ) is installed to the medium stacking plate  310 , in  FIG. 16  explained in the third embodiment, instead of the side parts  555   b ,  556   b  of respective extending parts  555 ,  556 , like the bias parts  355   c ,  355   e  and the bias parts  365   c ,  365   e  in  FIG. 4 , the bias parts  655   c ,  655   e  of the sheet guide  620  face and press the guide wall  342   a ; the bias parts  656   c ,  656   e  of the sheet guide  620  face and press the guide wall  341   a ; the bias parts  655   c ,  655   e  of the sheet guide  621  face and press the guide wall  343   a ; and the bias parts  656   c ,  656   e  of the sheet guide  621  face and press the guide wall  344   a.    
         [0112]    In the above mentioned configuration, since method of setting recording sheets on the medium stacking device is identical to that of the above mentioned third embodiment, the explanation of the method will be herein omitted. 
         [0113]    When a set recording sheet is carried in the direction of arrow A, for example, in a case where a sheet leading side (side of direction of arrow A) of the restriction surface  351  of the sheet guide  621  shown in  FIG. 18  is pressed by the pressure force Fc 1  due to skew of the recording sheet stacked on the medium stacking device, since forces are respectively led to a direction where the bias part  655   e  presses the guide wall  342   a  and the bias part  656   e  presses the guide wall  341   a , a restrative force Fa 4  generated from the bias part  655   e  and a restrative force Fa 2  generated from the bias part  656   e  respectively resist these forces. Thereby, an incline of the sheet guide  620  with respect to the direction of arrow A can be restricted. 
         [0114]    In the same manner, in a case where a sheet trailing side (opposite side of direction of arrow A) of the restriction surface  351  of the sheet guide  620  shown in  FIG. 18  is pressed by the pressure force Fc 2  due to skew of the recording sheet stacked on the medium stacking device, since the front edge part  656   h  of the side part  656   a  of the extending part  656  functions as a fulcrum, forces are respectively led to a direction where the bias part  655   c  presses the guide wall  342   a  and the bias part  656   c  presses the guide wall  341   a , a restrative force Fa 3  generated from the bias part  655   c  and a restrative force Fa 1  generated from the bias part  656   c  respectively resist these forces. Thereby, an incline of the sheet guide  620  with respect to the direction of arrow A can be restricted. Such a mechanism of prevention of incline of the sheet guide  621  disposed so as to face the sheet guide  620  is similar to the above mentioned mechanism. 
         [0115]    As mentioned above, according to the medium stacking device of the embodiment, even if skew is generated in the carried recording sheet, thereby, since an incline of the sheet guide  620 ,  621  is suppressed with respect to the sheet carrying direction (the direction of arrow A), and the skew of the recording sheet can be diminished. Furthermore, according to the explanation on  FIG. 10  of the first embodiment mentioned above, respectively, one of the extending part  656  and the extending part  655  is disposed in the direction of arrow A side and the other is disposed in the opposite side of the direction of arrow A side based on the center of the restriction surface  351  in the direction of arrow A. Thereby, the above mentioned effects of the embodiment can be more efficiently obtained regardless of directions of skew. 
         [0116]    Note, in the embodiment, the sheet guide to which the two extending parts are provided is shown as an example. However, same effects can be obtained by a sheet guide having two or more extending parts. 
         [0117]    Through the specification, a pair of racks ( 355 ,  356 ), a pair of extending parts ( 555 ,  556 ), and another pair of extending parts ( 655  and  656 ) are disclosed as the restriction members for the movement restriction parts. However, the restriction members are not necessarily only two components, but may be three or more components which function to regulate the movement of the sheet guide. 
         [0118]    In the above mentioned embodiments, applications of the present invention to an electrographic printer are explained. However, the present invention is not limited to the embodiments and may be applied to a multifunction printer (MFP), a facsimile device, a photocopy machine, and the like. In addition, in the above mentioned embodiments, applications of the present invention to manual feed trays are explained. However, the present invention may be applied to a cassette tray, an Auto Document Feeder (ADF), and the like.