PATENT ABSTRACT
The objective of the present invention is to provide a headrest that can have increased comfort and safety. This headrest is provided with: an affixed-side member provided to a headrest pillar; a mobile-side member that is joined to the affixed-side member with a mobile mechanism therebetween and that can move in the front-back direction with respect to the affixed-side member; and a front-back locking mechanism that has an engaged section and a lock member that engages the engaged section, and that locks and unlocks the movement of the mobile-side member in the front-back direction. Also, the mobile-side member has a front-side cover for supporting a head. Furthermore, the engaged section is attached to the back surface of the front-side cover.

PATENT DESCRIPTION
[0001]    This is a continuation application of application Ser. No. 14/758,282 filed Jun. 29, 2015 which is a U.S. National Phase of PCT/JP2012/084168 filed Dec. 28, 2012. The disclosures of the prior applications are hereby incorporated by reference herein in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a headrest. 
       BACKGROUND ART 
       [0003]    A headrest of a vehicle seat is provided to improve the level of comfort and safety through the support of a head of a person who sits on the seat. 
         [0004]    Patent Literature 1 discloses a headrest including a rear unit fixed to headrest pillars, and a front unit that is connected to the rear unit with a pair of X link members of a linkage and moves apart from the rear unit upon a rear-end collision. The movement of the front unit of the headrest apart from the rear section is caused by an unlocking operation of a solenoid in response to the rear-end collision. 
         [0005]    Such a headrest, which includes the X link members functioning as diagonal supports, has sufficient strength against the stress of a head pushing back the front unit of the headrest. 
       CITATION LIST 
     Patent Literature 
       [0006]    Patent Literature 1: Japanese Patent No. 4280589 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0007]    The level of comfort and safety offered by the headrest of the seat depends greatly on whether the headrest is at an appropriate position with respect to the head of the person who sits on the seat. 
         [0008]    The headrest described in Patent Literature 1 has the front unit which moves only upon the rear-end collision. The position of the front unit (hereafter referred to as a movable-side member) of the headrest cannot be adjusted in the front and back directions under normal conditions. The comfort and the safety offered by the headrest have been desired to be compatible 
         [0009]    An object of the present invention is to provide a headrest which can enhance the comfort and the safety. 
       Solution to Problems 
       [0010]    In order to solve the above problems, various embodiments of a headrest includes an affixed-side member which is arranged at a headrest pillar; a movable-side member which is connected to the affixed-side member via a moving mechanism and which moves in front and back directions with respect to the affixed-side member; and a front-back locking mechanism including a to-be-engaged unit and a lock member which engages with the to-be-engaged unit, the front-back locking mechanism locking and unlocking movement of the movable-side member in the front and back directions, wherein the movable-side member includes a front cover which supports a head, and the to-be-engaged unit is attached on a back surface of the front cover. 
         [0011]    In various embodiments of the headrest, a plurality of the to-be-engaged units are provided, and the plurality of the to-be-engaged units are arranged at position so that the moving mechanism is to be arranged therebetween. 
         [0012]    In various embodiments of the headrest, the moving mechanism is formed in a linkage mechanism, the front cover includes supporting units which rotatably support link members which constitute the linkage mechanism, and connecting members, which rotatably connect end parts of the link members to the supporting units, are provided so as to penetrate the to-be-engaged unit, the link members and the supporting units. 
         [0013]    In various embodiments of the headrest, the linkage mechanism is a X linkage mechanism including a first link member and a second link member which are rotably connected via a center cross connection unit, and the supporting units of the front cover are arranged on both sides of the front cover in up and down directions, a front end of the first link member and a front end of the second link member are rotatably supported by the upper and lower supporting units, and the connecting members are provided so as to respectively penetrate the supporting units. 
         [0014]    In various embodiments of the headrest, through holes in which the connecting members go through are respectively formed at the upper and lower supporting units, one of the through holes of the upper and lower supporting units is an elongated hole which is elongated in the up and down directions, the to-be-engaged unit includes: a plurality of teeth which are arranged in front and back directions; and upper and lower attaching units which are attached to the front cover, through holes in which the connecting members go through being formed in the upper and lower attaching units, one of the through holes of the upper and lower attachment units is an elongated hole which is elongated in the up and down directions, and the one of the through holes of the attaching units and a tooth at very front among the plurality of teeth align in a vertical direction. 
         [0015]    In various embodiments of the headrest, the link members include a plurality of reinforcement units arranged at a plurality of parts of the link members, and at least one of the plurality of reinforcement units is formed in a honeycomb structure. 
         [0016]    In various embodiments of the headrest, the front cover includes a reinforcement rib which is arranged on a back surface of the front cover, and the reinforcement rib and the front end parts of the link members are arranged on left and right sides of each other. 
         [0017]    In various embodiments of the headrest, the headrest pillar includes a pair of pillars, the affixed-side member includes: a pair of pillar holding units which are arranged on both side end parts of the affixed-side member and which respectively hold the pillars of the headrest pillar forming the pair; and a connector which connects between the upper ends of the pillar holding units forming the pair. 
         [0018]    In various embodiments of the headrest, a part of the affixed-side member which is surrounded by the pillar holding units forming the pair and the connector is a concave unit, and when the affixed-side member and the movable-side member are close to each other, the moving mechanism is to be housed in the concave unit. 
         [0019]    In various embodiments of the headrest, the to-be-engaged unit is projected toward the affixed-side member from the back surface of the front cover, a through hole is formed in the affixed-side member at a position corresponding to the to-be-engaged unit, the to-be-engaged unit being inserted in the through hole, and a wall which faces the to-be-engaged unit is provided at a circumference of the through hole. 
       Advantageous Effects of Invention 
       [0020]    According to various embodiments of the invention, the front-back positional adjustment of the movable-side member using the to-be-engaged units and supporting of the heat by the to-be-engaged units at the time collision are compatible. Therefore, the level of comfort and security of the seat when a passenger sits thereon can be improved. 
         [0021]    According to various embodiments of the invention, since the plurality of the to-be-engaged units are arranged at a plurality of parts having the moving mechanism therebetween, operation of the moving mechanism and the front-back locking mechanism can be carried out in a good balance. Further, since the head can be supported by the plurality of the to-be-engaged units, the level of security can be improved. 
         [0022]    According to various embodiments of the invention, since the connecting members are used to connect the to-be-engages units, the link members and the supporting units and used as rotary shafts, the number of parts needed can be reduced due to sharing the parts. 
         [0023]    According to various embodiments of the invention, even if the parts to be connected increase, they can be connected by the connecting members. Therefore, the effect of reduction in the number of parts due to sharing can be improved even more. 
         [0024]    According to various embodiments of the invention, the length in the up and down directions of the part near the upper end of the elongated hole of one of the attachment units can be made longer for the part corresponding to the very front teeth. Therefore, rigidity of one of the attachment units can be improved. 
         [0025]    According to various embodiments of the invention, by forming at least one of the plurality of reinforcement units of the link member in the honeycomb structure, the link member can be lightened and reinforced so as not to bend easily. 
         [0026]    According to various embodiments of the invention, interference between the reinforcement rib of the front cover and the front end part of the link member can be prevented, and rigidity of the front cover can be improved by the reinforcement rib. 
         [0027]    According to various embodiments of the invention, the upper end parts of the pair of pillar holding units can be connected by the connector. Therefore, the connecting condition of the pillar holding units forming the pair can be improved and rigidity of the affixed-side member can be improved. 
         [0028]    According to various embodiments of the invention, since the moving mechanism can be housed in the concave unit, the space between the affixed-side member and the movable-side member can be used efficiently, and the headrest can be formed in a compact manner. 
         [0029]    According to various embodiments of the invention, the projecting tips of the to-be-engaged units which are inserted in the through holes are held by the affixed-side member in which the through holes are formed. Further, since the to-be-engaged units can be supported by the walls which face the to-be-engaged units, stability of the movable-side member at the time of front-back positional adjustment can be improved. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0030]      FIG. 1  is a perspective view showing an inner mechanism of a headrest. 
           [0031]      FIG. 2  is a perspective view showing a headrest in a state where a front cover and a back cover are attached. 
           [0032]      FIG. 3  is a perspective view showing a headrest in a state where the back cover is attached. 
           [0033]      FIG. 4  is a perspective view showing the back surface side of the front cover and a rotary operation member. 
           [0034]      FIG. 5  is a perspective view showing the back surface side of the front cover and a to-be-engaged unit. 
           [0035]      FIG. 6  is a back view showing the inner structure and an operation unit of the headrest. 
           [0036]      FIG. 7  is a cross-sectional view showing an inner structure of the headrest. 
           [0037]      FIG. 8  is a perspective view showing an inner structure of the headrest before movement. 
           [0038]      FIG. 9  is a side view showing the inner structure of the headrest before movement. 
           [0039]      FIG. 10  is a perspective view showing the inner structure of the headrest after movement. 
           [0040]      FIG. 11  is a side view showing the inner structure of the headrest after movement. 
           [0041]      FIG. 12  is an enlarged front view showing a section near a through hole formed in an affixed-side member. 
           [0042]      FIG. 13  is a perspective view showing the front surface side of the back cover. 
           [0043]      FIG. 14  is an outline view showing another example of a biasing unit. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0044]    Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 
         [0045]    As shown in  FIGS. 1 to 11 , a headrest  1  of the embodiment includes a headrest pillar  2  having a pair of pillars  2   a  and  2   b , a pair of holder units  3  and  3 , an affixed-side member  4 , a moveable-side unit  5 , a moving mechanism, a front-back locking mechanism, an up-down locking mechanism and an operation unit  9 . The headrest  1  further includes a cushion pad and an outer layer material which are arranged around the headrest  1 . 
         [0046]    The headrest  1  is attached to the upper end part of a seatback of a vehicle seat. 
         [0047]    Here, in the embodiment, the front, back, up, down, left and right directions comply with the direction of the vehicle seat and the vehicle. 
         [0048]    The pair of holders  3  and  3  are to be attached to a seatback frame which is the framework of the seatback. 
         [0049]    The pair of pillars  2   a  and  2   b  of the headrest pillar  2  extend downward from the headrest  1  and are held by the pair of holder units  3  and  3 . That is, the headrest  1  is attached to the seatback frame via the pair of pillars  2   a  and  2   b  and the pair of holder units  3  and  3 . 
         [0050]    The pillars  2   a  and  2   b  forming a pair have the same diameter, and at least one of the pillars  2   a  and  2   b  forming a pair has a plurality of cutouts  15  along the length direction with spaces therebetween. 
         [0051]    The pillars  2   a  and  2   b  forming a pair are respectively held by the holder units  3  and  3  forming a pair. The pillars  2   a  and  2   b  are movable in the up and down directions along the holder units  3  and  3  forming a pair. 
         [0052]    Each of the holder units  3  and  3  forming a pair includes a cylindrical main body  3   a  which holds either of the pillars  2   a  and  2   b  forming a pair, a cover body  3   b  which covers the cylindrical main body  3   a  and a head unit  3   c  which is provided at the upper end part of the cylindrical main body  3   a.    
         [0053]    Further, each head unit  3   c  includes a lock unit  3   d  which prevents either of the pillars  2   a  and  2   b  forming a pair from slipping out by engaging with the plurality of cutouts  15  of either of the pillars  2   a  and  2   b  forming a pair. 
         [0054]    The pillars  2   a  and  2   b  forming a pair include projecting units  2   c  and  2   c  which slide freely along slits  20   a  and  20   b  of the after-mentioned affixed-side member  4  in a state where the pillars  2   a  and  2   b  forming a pair respectively being inserted in the pillar inserting holes  20  and  20  of the after-mentioned affixed-side member  4 . The projecting units  2   c  and  2   c  function as so-called rotation stoppers which prevent the pillars  2   a  and  2   b  forming a pair from rotating in the circumferential direction. 
         [0055]    The projecting units  2   c  and  2   c  project more outward than the side surfaces of the affixed-side member  4 . 
         [0056]    With respect to the affixed-side member  4 , the pillars  2   a  and  2   b  forming a pair are respectively arranged at the left and right end parts thereof. The affixed-side member  4  is to be attached to the seatback frame via the pair of pillars  2   a  and  2   b.    
         [0057]    The affixed-side member  4  is movable in the up and down directions along the pair of pillars  2   a  and  2   b.    
         [0058]    The movable-side member  5  is movable in the front and back directions with respect to the affixed-side member  4  and is connected with the affixed-side member  4  via the moving mechanism. In particular, the moveable-side member  5  is connected with the affixed-side member  4  via the moving mechanism and is movable in the front direction, which is the direction parting from the affixed-side member  4 , and in the back direction, which is the direction returning toward the affixed-side member  4 . 
         [0059]    The moveable-side member  5  includes a front cover  30  and a back cover  31  which can house individual parts including the affixed-side member  4 , the moving mechanism, the upper parts of the pillars  2   a  and  2   b  forming a pair, etc. 
         [0060]    The moving mechanism connects the affixed-side member  4  and the moveable-side member  5 , and for example, a link mechanism is adopted. In the embodiment, in particular, an X linkage mechanism is adopted. The X linkage mechanism includes a first link member  6  (hereinafter, an inner-side link member  6 ) and a second link member  7  (hereinafter, an outer-side link member  7 ) which are connected to each other so as to rotate via a center cross connection unit  8 . 
         [0061]    The front-back locking mechanism locks and unlocks the movement of the moveable-side member  5  in the front and back directions with respect to the affixed-side member  4 . The front-back locking mechanism includes to-be-engaged units  10 , a locking member  11  which engages with the to-be-engaged units  10 , biasing units  12  which bias the locking member  11  toward the to-be-engaged units  10  and a rotary operation member  13  which is held by the moveable-side member  5  so as to rotate freely and which operates the locking member  11 . 
         [0062]    The up-down locking mechanism locks and unlocks the affixed-side member  4  with respect to the pair of pillars  2   a  and  2   b  at any of the plurality of positions in the up and down directions. The up-down locking mechanism includes the after-mentioned up-down locking member  14 . 
         [0063]    The operation unit  9  is exposed from the outer surface of the headrest  1  and is for operating the front-back locking mechanism and the up-down locking mechanism at the same time. In particular, via the rotary operation member  13 , operations to unlock the locked state of the moveable-side member  5  wherein the moveable-side member  5  is prevented from moving in the front and back directions and operation to unlock the locked state of the affixed-side member  4  wherein the affixed-side member  4  is prevented from moving in the up and down directions are carried out. 
         [0064]    The operating direction of the operation unit  9  is along the width direction in the right and left directions. Operation of the operation unit  9  itself is carried out manually or automatically. In the embodiment, an embodiment of manual operation is adopted. 
         [0065]    The operation unit  9  of the embodiment is a button  9  which is pushed inside the headrest  1  to operate the front-back locking mechanism and the up-down locking mechanism. 
         [0066]    Next, the affixed-side member  4 , the moveable-side member  5  and the X linkage mechanism will be described in detail. 
       (Affixed-Side Member) 
       [0067]    The affixed-side member  4  is made of resin. As shown in  FIGS. 1 and 6 , for example, the affixed-side member  4  is formed in a block shape and includes a pair of pillar holding units  4   a  and  4   b , aback side connector  4   c , a connector  4   d , a plurality of supporting units  25  and  26 , a plurality of reinforcement units  27  . . . and a lock holding unit  28 . With respect to the affixed-side member  4 , all parts are formed integrally. 
         [0068]    The pillar holding units  4   a  and  4   b  forming a pair are arranged at the right and left end parts of the affixed-side member  4 , the pillar holding units  4   a  and  4   b  constituting the right and left sides of the affixed-side member  4 . The pillar holding units  4   a  and  4   b  forming a pair respectively hold the pillars  2   a  and  2   b  forming a pair. By having such configuration, the affixed-side member  4  is movable in the up and down directions along the pair of pillars  2   a  and  2   b.    
         [0069]    The pillar holding units  4   a  and  4   b  forming a pair respectively have pillar insertion holes  20  and  20  which bore through the pillar holding units  4   a  and  4   b  forming a pair in their length direction (up and down directions), and the pillars  2   a  and  2   b  forming a pair are to be inserted therein. 
         [0070]    On both sides of the affixed-side member  4 , that is, on side surfaces of the pillar holding units  4   a  and  4   b  forming a pair, slits  20   a  and  20   a  which communicate with the pillar insertion holes  20  and  20  are respectively formed along the up and down directions. 
         [0071]    The projecting units  2   c  and  2   c  of the pillars  2   a  and  2   b  forming a pair are to be arranged in the slits  20   a  and  20   a , respectively. 
         [0072]    The back side connector  4   c  is arranged between the pillar holding units  4   a  and  4   b  forming a pair and is a board-like member which connects the pillar holding units  4   a  and  4   b  forming a pair. The back surface of the back side connector  4   c  is flush with the back surfaces of the pillar holding units  4   a  and  4   b  forming a pair. 
         [0073]    On the back surface of the back side connector  4   c , a holding unit  21  which holds a to-be-held unit  70  of the after-mentioned lock member  11  is arranged. The holding unit  21  has an upward hook-like shape when seen from a side and is formed in an elongated shape along the right and left directions of the back side connector  4   c.    
         [0074]    The connector  4   d  is arranged between the upper end parts of the pillar holding units  4   a  and  4   b  forming a pair and is formed in a board-like body that connects between the upper end parts of the pillar holding units  4   a  and  4   b  forming a pair. The upper surface of the connector  4   d  is flush with the upper surfaces of the pillar holding units  4   a  and  4   b  forming a pair. 
         [0075]    The part of the affixed-side member  4  where surrounded by the pair of pillar holding units  4   a  and  4   b  and the connector  4   d  is a concave unit  22  which is formed in a concave shape. In particular, the concave unit  22  is the space between the surfaces of the pillar holding units  4   a  and  4   b  forming a pair that face each other, front side of the back side connector  4   c  and under the connector  4   d.    
         [0076]    As shown in  FIG. 3 , the moving mechanism is to be housed in the concave unit  22  in a state where the affixed-side member  4  and the movable-side member  5  are close to each other. 
         [0077]    As shown in  FIGS. 6, 8 and 10 , the back side connector  4   c  has through holes  23   a  and  23   b  at positions corresponding to first protruding units  60  and second protruding units  61  (will be described later) of the to-be-engaged units  10  constituting the front-back locking mechanism, and the first protruding units  60  and the second protruding units  61  are respectively inserted in the through holes  23   a  and  23   b.    
         [0078]    As shown in  FIG. 12 , walls  24   a  and  24   b  facing the first protruding units  60  and the second protruding units  61  are arranged around the circumferences of the through holes  23   a  and  23   b . The walls  24   a  are arranged between the through holes  23   a  and  23   b  and the walls  24   b  are arranged so as to face the surfaces of the pair of pillar holding units  4   a  and  4   b  that are facing each other. The surfaces of the pair of pillar holding units  4   a  and  4   b  that are facing each other also has the function similar as that of the walls  24   a  and  24   b.    
         [0079]    A plurality of supporting units  25  and  26  are connected with the inner-side link member  6  and the outer-side link member  7  which constitute the X linkage mechanism so that the inner-side link member  6  and the outer-side link member  7  rotate, and the plurality of supporting units  25  and  26  support the inner-side link member  6  and the outer-side link member  7 . 
         [0080]    The plurality of supporting units  25  and  26  are respectively arranged at the upper sides and the lower sides of the surfaces of the pair of pillar holding units  4   a  and  4   b  that are facing each other. That is, the plurality of supporting units  25  and  26  are respectively arranged at the four corners of the concave unit  22 . 
         [0081]    The supporting units  25  and  25  which are arranged at the upper side are formed integrally with the pair of pillar holding units  4   a  and  4   b , the back side connector  4   c  and the connector  4   d . The supporting units  26  and  26  which are arranged at the lower side are formed integrally with the pair of pillar holding units  4   a  and  4   b  and the back side connector  4   c.    
         [0082]    The plurality of upper side supporting units  25  and  25  respectively have through holes  25   a  in which a connecting member S is to be inserted, the through holes  25   a  being formed so as to penetrate the pair of pillar holding units  4   a  and  4   b  from the surfaces of the plurality of supporting units  25  on the concave unit  22  side. The through holes  25   a  of the plurality of upper side supporting units  25  and  25  are round holes. 
         [0083]    The connecting member S is inserted in the round hole  25   a  which is opened on the side of the pillar holding unit  4   a  ( 4   b ) which is one of the pair of pillar holding units  4   a  and  4   b  so as to connected the link member  6  ( 7 ). 
         [0084]    The connecting members S connect the inner-side link member  6  and the outer-side link member  7  to the plurality of supporting units  25  and  26  so as to rotate. In the embodiment, metallic shafts (rotary shafts) are used. That is, the connecting member S is arranged so as to go through the link member  6  ( 7 ) and the supporting units  25  and  25 . 
         [0085]    The plurality of lower side supporting units  26  and  26  are formed to be longer in the up and down directions comparing to the plurality of upper side supporting units  25  and  25 . 
         [0086]    The plurality of supporting units  26  and  26  respectively have through holes  26   a  in which a connecting member S is to be inserted, the through holes  26   a  being formed on the surfaces of the plurality of supporting units  26  and  26  in the concave unit  22  side. The holes  26   a  of the plurality of lower side supporting units  26  and  26  are elongated holes (slits) which are elongated in the up and down directions along the plurality of lower side supporting units  26  and  26 . 
         [0087]    Parts  26   b  of the elongated holes  26   a  are formed so as to penetrate the pillar holding units  4   a  and  4   b  forming a pair. The parts  26   b  of the elongated holes  26   a  are round holes. The connecting member S is inserted from the part  26   b  of the elongated hole  26   a  which opens on a side of the pillar holding unit  4   a  ( 4   b ) which is one of the pillar holding units  4   a  and  4   b  forming a pair so as to connect the link member  7  ( 6 ). The connecting member S is arranged so as to go through the link member  7  ( 6 ) and the supporting units  26  and  26 . 
         [0088]    The plurality of reinforcement units  27  . . . are arranged at a plurality of parts in the affixed-side member  4 . Among the plurality of reinforcement units  27 , at least one is formed in a honeycomb structure. 
         [0089]    In the embodiment, the front surfaces and the back surfaces of the pillar holding units  4   a  and  4   b  forming a pair are the reinforcement units  27  having the honeycomb structure. By forming at least one of the plurality of the reinforcement units  27  of the affixed-side member  4  in the honeycomb structure, the affixed-side member  4  can be lighter and can be reinforced so that it is not easily bent. 
         [0090]    Although it is not the honeycomb structure, a reinforcement unit  27  is also formed in the upper surface of the connector  4   d . The reinforcement unit  27  of the connector  4   d  has ribs arranged in a grid pattern. 
         [0091]    The lock holding units  28  hold the up-down locking member  14  which constitutes the up-down locking mechanism and are respectively arranged near the lower ends of the pillar holding units  4   a  and  4   b  forming a pair. The up-down locking member  14  is provided at either one of the pillar holding units  4   a  and  4   b  forming a pair. In the embodiment, the up-down locking member  14  is arranged on the left side of the headrest  1 . 
         [0092]    The lock holding unit  28  has an opening  28   a  formed on a side and the up-down locking member  14  is provided through the opening  28   a.    
         [0093]    With respect to the lock holding unit  28  on the side which the up-down locking member  14  is not provided, the pillar  2   b  ( 2   a ) can be seen through the opening  28   a  on the side. 
         [0094]    Further, the lock holding units  28  are provided with catch units  28   b  to which the hook units  12   a  of the biasing units  12  (after-mentioned) are to be hooked. The catch units  28   b  of the embodiment are hole units which are formed in the under surface of the front parts of the lock holding units  28 . 
       (Movable-Side Member) 
       [0095]    The movable-side member  5  is arranged on the side of the passenger&#39;s head and can be moved in the front and back directions with respect to the affixed-side member. In particular, as shown in  FIGS. 2 to 5  and  FIGS. 7 to 11 , the movable-side member  5  is movable in the front and back with respect to the affixed-side member  4 . 
         [0096]    The movable-side member  5  is made of resin. The movable-side member  5  includes a front cover  30 , a back cover  31 , lower edge covers  32  and  32 , a holding unit  33 , a button attaching unit  34 , a plurality of supporting units  35  and  36 , a reinforcement rib  37  and concave units  38  and  38 . With respect to the movable-side member  5 , the front cover  30 , the back cover  31  and the lower edge covers  32  and  32  are formed separately. 
         [0097]    By assembling the front cover  30  and the back cover  31 , a hollow case body can be formed. 
         [0098]    The front cover  30  is provided to support the head. The front cover  30  includes a front side unit  30   a  and a surrounding unit  30   b  which is provided toward the back from the surrounding edges (up, down, left and right) of the front side unit  30   a . The parts constituting the front cover  30  are formed integrally. 
         [0099]    As shown in  FIGS. 4 and 5 , ribs for reinforcing the boundary parts of the front side unit  30   a  and the surrounding unit  30   b  are arranged as needed between the back side of the front side unit  30   a  and the surrounding unit  30   b.    
         [0100]    The back cover  31  includes a back side unit  31   a  and a surrounding unit  31   b  which is provided toward the front from the surrounding edges (up, down, left and right) of the back side unit  31   a . The case body is constituted by connecting and fixating the surrounding unit  31   b  of the back cover  31  and the surrounding unit  30   b  of the front cover  30  together. 
         [0101]    By adapting a fitting mechanism, the surrounding unit  30   b  and the surrounding unit  31   b  are connected by being fitted to each other. However, this is not limitative in anyway. Any known technique can be adopted. 
         [0102]    As shown in  FIG. 13 , the back cover  31  is arranged at the position corresponding to the tips of the first protruding units  60  and the tips of the second protruding units  61  of the to-be-engaged unit  10  (after-mentioned), and the back cover  31  is provided with tip housing units  31   d  and  31   d  in which the above mentioned tips are to be housed. 
         [0103]    The tip housing units  31   d  and  31   d  are formed so as to protrude from the front surface of the back cover  31 . The tip housing units  31   d  and  31   d  respectively includes wall units  31   e  which surround the tips of the first protruding units  60  and the tips of the second protruding units  61  and slits  31   f  which prevent the to-be-held units  70  of the lock member  11  (after-mentioned) from interfering with the wall units  31   e.    
         [0104]    The lower edge covers  32  and  32  are respectively fitted to the two elongated holes (will be described later) which are formed in the lower surface of the case body which is formed by connecting the front cover  30  and the back cover  31 . Each lower edge cover  32  includes a cylindrical unit  32   a  which is to be inserted in an elongated hole and a collar unit  32   b  which is arranged at the lower edge unit of the cylindrical unit  32   a  and abuts the lower surface of the case body. 
         [0105]    The lower surfaces of the surrounding unit  30   b  and the surrounding unit  31   b  include cutouts units  30   c  and  31   c  for inserting the pair of pillars  2   a  and  2   b  and the lower edge covers  32  and  32 . Each of the cutout units  30   c  and  31   c  is formed in a shape where an elongated hole is cut in half. Elongated holes are to be formed in the lower surface of the case body by the surrounding unit  30   b  and the surrounding unit  31   b  being connected to each other. 
         [0106]    Two elongated holes are formed in the lower surface of the case body, and the elongated holes are arranged so that they are elongated along the front-to-back moving direction of the movable-side member  5 . The cylindrical units  32   a  are also arranged so that they are elongated along the front-to-back moving direction of the movable-side member  5 . 
         [0107]    The holding unit  33  is for holding the rotary shaft unit  82  of the rotary operation member  13  (after-mentioned). As shown in  FIGS. 4 and 5 , the holding unit  33  is provided inside (in the inside space of the case body) the surrounding unit  30   b  of the front cover  30  on either left or right side thereof. 
         [0108]    The holding unit  33  includes a plurality of upper abutting units  33   a  which abut the rotary shaft unit  82  from above and a lower abutting unit  33   b  which abuts the rotary shaft unit  82  from below. The upper abutting units  33   a  include a plurality of claw units  33   c  and  33   c  which are the tip parts of the upper abutting units  33   a.    
         [0109]    The upper abutting units  33   a  and the lower abutting unit  33   b  are formed so as to protrude toward the back cover  31  side from the front cover  30  side. 
         [0110]    As shown in  FIGS. 2 to 5 , the button attaching unit  34  is for attaching the button  9  which is the operation unit  9  to the front cover  30  and the back cover  31 . The button attaching unit  34  is arranged at one side of the front cover  30  and the back cover  31 . 
         [0111]    The button attaching unit  34  is a cylindrical body which protrudes from a side of the front cover  30  and the back cover  31 . The button attaching unit  34  includes a cylindrical front unit  34   a  which is arranged on the front cover  30  side, a cylindrical back unit  34   b  which is arranged on the back cover  31  side and a ring-shaped button holding unit  34   c  which is arranged inside the front cover  30  and holds the button  9 . 
         [0112]    The button  9  is to be surrounded by the cylindrical front unit  34   a  of the front cover  30  and the cylindrical back unit  34   b  of the back cover  31  in a state where the button  9  is being held by the button holding unit  34   c . In such way, the button  9  is attached to the button attaching unit  34 . 
         [0113]    To the plurality of supporting units  35  and  36 , the inner-side link member  6  and the outer-side link member  7  which constitute the X linkage mechanism are connected so as to rotate. The plurality of supporting units  35  and  36  support the inner-side link member  6  and the outer-side link member  7 . 
         [0114]    The plurality of supporting units  35  and  36  are arranged at the positions in the back surface of the front cover  30  corresponding to the front edges of the inner-side link member  6  and the outer-side link member  7 . The plurality of supporting units  35  and  36  are arranged on both sides in the left and right directions (width) and both sides of the up and down directions on the back surface of the front cover  30 . That is, the plurality of supporting units  35  and  36  are arranged at the four positions on the back surface of the front cover  30 . 
         [0115]    The front edges of the outer-side link member  7  are connected to the supporting units  35  and  35  which are arranged at the upper side and the front edges of the inner-side link member  6  are connected to the supporting units  36  and  36  which are arranged at the lower side. 
         [0116]    On the surfaces of the plurality of supporting units  35  and  35  on the upper side that face each other, protruding units  35   b  and  35   b  which protrude toward the surfaces facing each other are respectively formed integrally. The protruding units  35   b  are for attaching the to-be-engaged unit  10  to the supporting units  35 , and the protruding units  35   b  are to be engaged with the through holes  63   a  of the to-be-engaged unit  10  (after-mentioned). 
         [0117]    The outside diameter of the protruding units  35   b  is set to be slightly smaller than the inside diameter of the through holes  63   a  and is set to be smaller than the diameter of the edges of the surfaces of the supporting units  35  which face each other. 
         [0118]    On the surfaces of the plurality of lower side supporting units  36  and  36  that face each other, protruding units  36   b  and  36   b  which protrude toward the surfaces facing each other are respectively formed integrally. The protruding units  36   b  are for attaching the to-be-engaged unit  10  to the supporting units  36 , and the protruding units  36   b  are to be engaged with the through holes  64   a  of the to-be-engaged unit  10  (after-mentioned). 
         [0119]    The outside diameter of the protruding units  36   b  is set to be slightly smaller than the inside diameter of the through holes  64   a  and is set to be smaller than the diameter of the edges of the surfaces of the supporting units  36  which face each other. 
         [0120]    In the plurality of upper side supporting units  35  and  35  and the protruding units  35   b  and  35   b , through holes  35   a  in which the connecting member S is to be inserted are formed so as to penetrate in the left and right directions (width). Here, the through holes  35   a  of the plurality of upper side supporting units  35  and  35  are round holes. 
         [0121]    On the left and right surfaces of the surrounding unit  30   b  of the front cover  30 , through holes  30   d  and  30   d  are respectively formed at the positions on the lines extending from the through holes  35   a  and  35   a  of the plurality of upper side supporting units  35  and  35 . 
         [0122]    The connecting member S is inserted through the through holes  35   a  of the plurality of supporting units  35  and  35  and the protruding unit  35   b  and  35   b  from either one of the through holes  30   d  in the left and right side surfaces of the front cover  30  so as to connect the link member  7  ( 6 ) to the plurality of supporting units  35  and  35 . That is, the connecting member S is arranged so as to go through the link member  7  ( 6 ), the supporting units  35  and  35  and the to-be-engaged units  10  and  10  which are attached to the supporting units  35  and  35 . 
         [0123]    The plurality of supporting units  36  and  36  and the protruding units  36   b  and  36   b  on the lower side are formed in elongated shapes elongated in the up and down directions comparing to the plurality of supporting units  35  and  35  and the protruding units  35   b  and  35   b  on the upper side. 
         [0124]    In the plurality of lower side supporting units  36  and  36  and the protruding units  36   b  and  36   b , the through holes  36   a  in which the connecting member S (after-mentioned) is to be inserted is formed so as to penetrate in the left and right directions (width). Here, the through holes  36   a  of the plurality of upper side supporting units  36  and  36  and the protruding units  36   b  and  36   b  are elongated holes elongated in the up and down directions along the supporting units  36  and  36 . 
         [0125]    On the left and right surfaces of the surrounding unit  30   b  of the front cover  30 , through holes  30   e  and  30   e  are respectively formed at the positions on the lines extending from the elongated through holes  36   a  and  36   a  of the plurality of lower side supporting units  36  and  36 . The through holes  30   e  and  30   e  are round holes arranged on the lines extending from the upper edges of the elongated through holes  36   a  and  36   a.    
         [0126]    The connecting member S is inserted through the through holes  36   a  of the plurality of supporting units  36  and  36  and the protruding unit  36   b  and  36   b  from either one of the through holes  30   e  on the left and right side surfaces of the front cover  30  so as to connect the link member  6  ( 7 ) to the plurality of supporting units  36  and  36 . That is, the connecting member S is arranged so as to go through the link member  6  ( 7 ), the supporting units  36  and  36  and the to-be-engaged units  10  and  10  which are attached to the supporting units  36  and  36 . 
         [0127]    The reinforcement rib  37  is formed on the back surface of the front cover  30  at the center position between the plurality of supporting units  36  and  36 . 
         [0128]    The reinforcement rib  37  is formed so as to project toward the back, and the degree of its projection is set so as not to interfere with the connecting member S which is arranged at the plurality of the supporting units  36  and  36 . 
         [0129]    The part in the front surface of the front cover  30  corresponding to the part where the reinforcement rib  37  is formed is concaved corresponding to the projection of the reinforcement rib  37 . 
         [0130]    The reinforcement rib  37  and the front edges of the link (the inner-side link member  6  in the embodiment) are arranged in a line in the left and right sides of each other. That is, the reinforcement rib  37  is to be arranged between a first arm  40  and a second arm  41  of the inner-side link member  6  (after-mentioned). 
         [0131]    The concave units  38  and  38  are formed on the back surface of the front cover  30  at position corresponding to frontward protruding units  65  and  65  of the to-be-engaged units  10  and  10  (after-mentioned). 
         [0132]    The concave units  38  and  38  are arranged right above the plurality of lower side supporting units  36  and  36 . At the outer edges of the concave units  38  and  38 , the reinforcement ribs  38   a  and  38   a  are respectively formed integrally with the plurality of supporting units  36  and  36 . The reinforcement ribs  38   a  and  38   a  are respectively facing the front side protruding units  65  and  65  of the to-be-engaged units  10  and  10 . 
       (X Linkage Mechanism) 
       [0133]    As shown in  FIGS. 1, 3, 7 to 11 , in the X linkage mechanism, the inner-side link member  6  is a link in which the upper edge (back edge) thereof is arranged on the affixed-side member  4  side and the lower edge (front edge) thereof is arranged on the movable-side member  5  side. 
         [0134]    The outer-side link member  7  is a link in which the upper edge (front edge) thereof is arranged on the movable-side member  5  side and the lower edge (back edge) thereof is arranged on the affixed-side member  4  side. 
         [0135]    The front and back directions of the inner-side link member  6  and the outer-side link member  7  can be reversed. The X linkage mechanism is made of resin except for the connecting member S. 
         [0136]    The upper edge of the inner-side link member  6  is to be arranged between the plurality of upper side supporting units  25  and  25  which are arranged at the left and right sides in the affixed-side member  4 . 
         [0137]    The lower edge of the outer-side link member  7  is arranged between the plurality of lower side supporting units  26  and  26  which are arranged at the left and right sides in the affixed-side member  4 . 
         [0138]    The lower edge of the inner-side link member  6  is arranged between the plurality of lower side supporting units  36  and  36  which are arranged at the left and right sides in the movable-side member  5 . 
         [0139]    The upper edge of the outer-side link member  7  is arranged between the plurality of upper side supporting units  35  and  35  which are arranged at the left and right sides of the movable-side member  5 . 
         [0140]    As shown in  FIG. 7 , the inner-side link member  6  and the outer-side link member  7  are in a bent shape when seen from a side. 
         [0141]    The inner-side link member  6  and the outer-side link member  7  are connected via the center cross connection unit  8  so as to rotate. 
         [0142]    In the X linkage mechanism, a part where one link and the other link overlap is naturally formed. Therefore, the cross connection unit  8  is arranged at the part where the inner-side link member  6  and the outer-side link member  7  overlap with each other, the overlapping part being naturally formed when constituting the X linkage mechanism. 
         [0143]    The cross connection unit  8  is arranged on the line connecting the connecting members S and S respectively arranged at the upper edge and the lower edge of the inner-side link member  6  and on the line connecting the connecting members S and S respectively arranged at the upper edge and the lower edge of the outer-side link member  7 . 
         [0144]    In the inner-side link member  6  and the outer-side link member  7 , round holes which penetrate the inner-side link member  6  and the outer-side link member  7  are respectively formed at the parts corresponding to the cross connecting unit  8 . A connecting member S is inserted in the round holes. That is, the inner-side link member  6  and the outer-side link member  7  are connected to each other so as to rotate with the connecting member S being the rotary shaft. 
         [0145]    The inner-side link member  6  of the embodiment includes the first arm  40  and the second arm  41 . That is, the two arms  40  and  41  constitute the inner-side link member  6  of the embodiment. The inner-side link member  6  further includes a plurality of connections  42  which are arranged at the edge parts of the first arm  40  and the second arm  41 . 
         [0146]    The first arm  40  and the second arm  41  are formed so to be symmetrical and are arranged to face the same direction having a space between each other. The inside unit  51  of the outer-side link member  7  is arranged in the space between the first arm  40  and the second arm  41 . 
         [0147]    The first arm  40  includes reinforcement units  43  at both the left and right sides thereof and the second arm  41  includes reinforcement units  44  at both the left and right sides thereof. These reinforcement units  43  and  44  are not the honeycomb structure. The reinforcement units  43  and  44  have a plurality of ribs arranged therein. 
         [0148]    The plurality of connections  42  . . . are the upper and lower edges of the first arm  40  and the second arm  41 , and are the parts connected to the upper side supporting units  25  and  25  of the affixed-side member  4  and the lower side supporting units  36  and  36  of the movable-side member  5  and supported by the upper side supporting units  25  and  25  and the lower side supporting units  36  and  36 . 
         [0149]    Through holes are formed in the connections  42  and  42  at the upper edges of the first arm  40  and the second arm  41  so as to penetrate the connections  42  and  42 , in which the connecting member S is to be inserted, in the left and right directions (width). The through holes are round holes. 
         [0150]    Since the connecting members S is to be inserted in the through holes, the through holes are arranged on the line extending from the through holes  25   a  and  25   a  that are formed in the plurality of upper side supporting units  25  and  25  of the affixed-side member  4 . The connecting member S is inserted in the round holes of the upper side supporting units  25  and  25  and the round holes of the connections  42  and  42  at the upper edges. That is, the first arm  40  and the second arm  41  are connected to the affixed-side member  4  via the connecting member S so as to rotate, the connecting member S being the rotary shaft. 
         [0151]    Similarly, through holes (round holes) are formed in the connections  42  and  42  at the lower edge parts of the first arm  40  and the second arm  41 . 
         [0152]    The connecting member S is inserted in the plurality of the elongated holes  36   a  and  36   a  of the plurality of lower side supporting units  36  and  36  of the movable-side member  5  and the round holes of the connections  42  and  42  at the lower edges. That is, the first arm  40  and the second arm  41  are connected to the movable-member  5  via the connecting member S so as to rotate, the connecting member S being the rotary shaft. 
         [0153]    The connecting member S arranged at the connections  42  and  42  at the lower edges of the first arm  40  and the second arm  41  can move in the up and down directions along the elongated holes  36   a  and  36   a  formed in the plurality of lower side supporting units  36  and  36 . That is, the lower edges of the first arm  40  and the second arm  41  can move in the up and down directions along the lower side supporting units  36  and  36  according to the front-to-back movement of the movable-side member  5 . 
         [0154]    The reinforcement rib  37  is arranged between the connection  42  at the lower edge of the first arm  40  and the connection  42  at the lower edge of the second arm  41 . 
         [0155]    The outer-side link member  7  of the embodiment includes left and right side wall units  50  and  50 , an inside unit  51  arranged between the left and right side wall units  50  and  50 , a plurality of connections  52  . . . and a plurality of reinforcement units  53  . . . . The left and right side wall units  50  and  50 , the inside unit  51 , the plurality of connections  52  and  52  and the plurality of reinforcement units  53  . . . are formed integrally. 
         [0156]    The left and right side wall units  50  and  50  are the parts positioning outside of the first arm  40  and the second arm  41  of the inner-side link member  6 . The left and right side wall units  50  and  50  are arranged so as to intersect with the first arm  40  and the second arm  41  and sandwich the first arm  40  and the second arm  41 . 
         [0157]    The inside unit  51  is the part that intersects with the first arm  40  and the second arm  41  of the inner-side link member  6  and sandwiched by the left and right side wall units  50  and  50 . 
         [0158]    At the part of the inside unit  51  where intersects with the first arm  40  and the second arm  41 , arm inserting holes  51   a  and  51   a  in which the first arm  40  and the second arm  41  are to be inserted are formed. 
         [0159]    The arm inserting holes  51   a  and  51   a  are formed in a size in which the inside unit  51  does not interfere with the first arm  40  and the second arm  41  when the inner-side link member  6  and the outer-side link member  7  are folded. 
         [0160]    When the movable-side member  5  is returned to the affixed-side member  4  side, the inside unit  51  abuts the first arm  40  and the second arm  41 . The parts of the inside unit  51  where abut the first arm  40  and the second arm  41  are formed in a concaved shape (concave units  51   b ). When the movable-side member  5  is returned to the affixed-side member  4  side, the first arm  40  and the second arm  41  are to be housed in the concave units  51   b  of the inside unit  51 . In such way, the inner-side link member  6  and the outer-side link member  7  can be folded in a compact manner. 
         [0161]    The concave units  51   b  are formed respectively at the upper left and right edges of the inside unit  51  on its back surface and at the lower left and right edges of the inside unit  51  on its front surface. 
         [0162]    The plurality of connections  52  and  52  are the upper and lower edges of the outer-side link member  7  and are the parts that are connected to the lower side supporting units  26  and  26  of the affixed-side member  4  and the upper side supporting units  35  and  35  of the movable-side member  5  and supported by the lower side supporting units  26  and the upper side supporting unit  35  and  35 . 
         [0163]    Through holes in which the connecting member S is to be inserted are formed in the connections  52  and  52  so as to penetrate the connections  52  and  52  in the left and right directions (width). The through holes are round holes. 
         [0164]    The connecting member S is to be inserted in the through holes. Therefore, the through holes are respectively formed on the line extending from the through holes  26   a  and  26   a  which are formed in the plurality of lower side supporting units  26  and  26  of the affixed-side member  4  and on the line extending from the through holes  35   a  and  35   a  which are formed in the plurality of upper side supporting units  35  and  35  of the movable-side member  5 . 
         [0165]    The connecting member S is inserted in the elongated holes of the lower side supporting units  26  and  26  and the round holes of the connections  52  at the lower edges. 
         [0166]    The connecting member S which is arranged in the connections  52  at the lower edges can move in the up and down directions along the elongated holes  26   a  and  26   a  which are formed in the plurality of lower side supporting units  26  and  26 . That is, the lower edge of the outer-side link member  7  can move in the up and down directions along the lower side supporting units  26  and  26  according to the front-to-back movement of the movable-side member  5 . 
         [0167]    The connecting member S is inserted in the round holes of the upper side supporting units  35  and  35  and the round holes of the connections  52  at the upper edges. That is, the upper edge of the outer-side link member  7  is connected to the movable-side member  5  via the connecting member S so as to rotate, the connecting member S being the rotary shaft. 
         [0168]    The plurality of reinforcement units  53  are arranged at a plurality of parts in the outer-side link member  7 , and at least one of the plurality of reinforcement units  53  is formed in the honeycomb structure. 
         [0169]    In the embodiment, the plurality of reinforcement units  53  are arranged on the side of the outer-side link member  7  which is the opposite side of the side on which the concave units  51   b  are formed, that is, the plurality of reinforcement units  53  are arranged at the upper left and right edges on the front surface of the inside unit  51  and at the lower left and right edges on the back surface of the inside unit  51 . In the inside unit  51 , the reinforcement units  53  are provided on the back surface and the front surface at the upper sections of the part positioning between the first arm  40  and the second arm  41  of the inner-side link member  6 . 
         [0170]    In the embodiment, all of the reinforcement units  53  have the honeycomb structure. 
         [0171]    By adapting the above described configuration, the movable-side member  5  can be moved so as to apart from the affixed-side member  4  in the forward direction and so as to approach the affixed-side member  4  in the backward direction via the X linkage mechanism which is the moving mechanism. 
         [0172]    Next, the front-back locking mechanism and the up-down locking mechanism will be described in detail. 
       (Front-Back Locking Mechanism) 
       [0173]    As described above, the front-back locking mechanism includes the to-be-engaged units  10 , the locking member  11  which engages with the to-be-engaged units  10 , the biasing units  12  which bias the locking member  11  toward the to-be-engaged units  10 , and the rotary operation member  13  which operates the locking member  11 , the rotary operation member  13  being held at the movable-side member  5  so as to rotate freely. 
         [0174]    The to-be-engaged units  10  are made from metal, and as shown in  FIGS. 1, 3 and 5 , for example, the to-be-engaged units  10  are attached on the back surface of the front cover  30  and protrude toward the affixed-side member  4  from the back surface of the front cover  30 . 
         [0175]    A plurality of to-be-engaged units  10  are used and they are arranged so as to have the X linkage mechanism between them. 
         [0176]    Each of the to-be-engaged units  10  has the ratchet mechanism having a plurality of teeth  60   a  which are arranged in a line in the front and back directions. The plurality of teeth  60   a  are projected upward from below. 
         [0177]    Each to-be-engaged unit  10  includes the first protruding unit  60 , the second protruding unit  61 , a space  62 , attachment units  63  and  64  and the frontward protruding unit  65 . 
         [0178]    Each to-be-engaged unit  10  is formed in an approximately T-shape when seen from a side. That is, the first protruding unit  60  and the second protruding unit  61  are protruded in an approximately horizontal direction. The attachment unit  63  projects upward in approximately vertical direction and the attachment unit  64  projects downward in approximately vertical direction. 
         [0179]    Each of the first protruding units  60  has a plurality of teeth  60   a , and the to-be-engaged unit  10  is projected toward the affixed-side member  4  from the movable-side member  5  in a state being attached to the back surface of the front cover  30 . 
         [0180]    Each of the first protruding units  60  is arranged below the plurality of teeth  60   a  since the plurality of teeth  60   a  . . . which project upward from below are formed thereon. That is, the plurality of teeth  60   a  are formed so as to project upward from the upper edges of the first protruding units  60 . 
         [0181]    The tips of the first protruding units  60  are formed to have a taper shape and are to be housed in the tip housing units  31   d  of the back cover  31 . 
         [0182]    The second protruding units  61  are parallel to the first protruding units  60 , respectively, and are arranged so as to have spaces between the upper edges of the plurality of teeth  60   a . The spaces between the second protruding units  61  and the plurality of teeth  60   a  of the first protruding units  60  are the spaces  62 . 
         [0183]    The tips of the second protruding units  61  are to be housed in the tip housing units  31   d  of the back cover  31 . 
         [0184]    The through holes  63   a  and  64   a  in which the connecting members S are to be inserted are formed in the attachment units  63  and  64  and the attachment units  63  and  64  are attached to the front cover  30 . 
         [0185]    The attachment units  63  are formed so as to protrude upward from the base parts (front) of the second protruding units  61  and the attachment units  64  are formed so as to protrude downward from the base parts (front) of the first protruding units  60 . 
         [0186]    As described above, the through holes  63   a  are where the protruding units  35   b  and  35   b  of the plurality of upper side supporting units  35  and  35  are to be fitted, respectively. That is, by fitting the through holes  63   a  and the protruding units  35   b , respectively, the attachment units  63  can be attached to the back surface of the front cover  30 . 
         [0187]    Each attachment unit  63  has a slit  63   b  formed below the through hole  63   a . The slits  63   b  contribute to lightening of the to-be-engaged unit  10 . 
         [0188]    As described above, the through holes  64   a  are where the protruding units  36   b  and  36   b  of the plurality of lower side supporting units  36  and  36  are to be fitted, respectively. That is, by fitting the through holes  64   a  and the protruding units  36   b , respectively, the attachment units  64  can be attached to the back surface of the front cover  30 . 
         [0189]    The through holes  64   a  are elongated holes which are elongated in the up and down directions corresponding to the shapes of the supporting units  36  and the protruding units  36   b  and the shape of the through holes  36   a.    
         [0190]    As shown in  FIGS. 9 and 11 , in each attachment unit  64 , the through hole  64   a  and the tooth  60   a  at the front among the plurality of teeth  60   a  are aligned in the vertical direction. 
         [0191]    The frontward protruding units  65  position in front of the to-be-engaged units  10 , respectively, and they protrude frontward than the attachment units  63  and  64 . 
         [0192]    The frontward protruding units  65  are to be inserted respectively in the concave units  38  which are formed on the back surface of the front cover  30 , and are arranged so as to face the reinforcement ribs  38   a  which are arranged at the outer edges of the concave units  38 , respectively. 
         [0193]    The locking member  11  engages with a to-be-engaged unit  10  to constitute the main part of the front-back locking mechanism with the to-be-engaged unit  10 . As shown in  FIGS. 1, 3, 6 to 12 , the locking member  11  includes a to-be-held unit  70 , engaging units  71  and  71  and connecting units  72  and  72 . 
         [0194]    The to-be-held unit  70  is a metallic shaft and is to be held by the affixed-side member  4 . As shown in  FIGS. 6 and 7 , the to-be-held unit  70  is arranged at the back of the affixed-side member  4  and is held in a state being inserted in the holding unit  21  from the above, the holding unit  21  being arranged on the back surface of the affixed-side member  4 . 
         [0195]    The to-be-held unit  70  is arranged in the spaces  62  between the first protruding units  60  and the second protruding units  61 . The to-be-held unit  70  is arranged above the engaging units  71  and  71 . 
         [0196]    The two ends of the to-be-held unit  70 , there back surface sides, are inserted in the slits  31   f  of the tip housing units  31   d  of the back cover  31 . 
         [0197]    The engaging units  71  and  71  are metallic shafts, and they are arranged to be parallel to the to-be-held unit  70  and rotate around the to-be-held unit  70 , the to-be-held unit  70  being the shaft, and they are biased toward the plurality of teeth  60   a  to be engaged with any of the plurality of teeth  60   a . The engaging units  71  and  71  are arranged in front of the affixed-side member  4 . 
         [0198]    The engaging units  71  and  71  are arranged at the positions engaging with the plurality of teeth  60   a  by being biased by the biasing units  12 . As shown in  FIG. 12 , in a case where the engaging units  71  and  71  move in the direction opposite to the biasing direction of the biasing units  12 , the engaging units  71  and  71  are to move to the positions of the spaces  62 . 
         [0199]    With respect to the engaging units  71  and  71 , the tip parts (front edges) thereof on the plurality of teeth  60   a  sides are protruded inside than the to-be-engaged units  10  and  10 . However, the protruding lengths are set so as not to reach to the X linkage mechanism. 
         [0200]    The connecting units  72  and  72  are metallic shafts, and they connect the edges of the to-be-held unit  70  and the edges of the engaging units. The connecting units  72  and  72  are arranged on the left and right sides of the affixed-side member  4 . That is, the locking member  11  is formed in an approximately C shape so as to go around the circumference of the affixed-side member  4 . 
         [0201]    With respect to the connecting units  72  and  72 , a cover member  73  which covers one connecting unit  72  and ends of the to-be-held unit  70  and the engaging unit  71  on the connecting unit  72  side is attached integrally at the one connecting unit on the side where the rotary operation member  13  is to be arranged. That is, the one connecting unit  72  includes the cover member  73 . 
         [0202]    As shown in  FIG. 6 , the cover member  73  of the connecting unit  72  abuts a side surface of the affixed-side member  4 . 
         [0203]    The cover member  73  of the embodiment covers one of the connecting units  72 . However, the cover member  73  may be configured as a member where one end of the to-be-held unit  70  and one end of the engaging unit  71  are to be attached. 
         [0204]    The cover member  73  of the connecting unit  72  includes a projecting abutting unit  74  which projects toward the rotary operation member  13  side and abuts the rotary operation member  13 , the projecting abutting unit  74  being arranged at the part of the cover member  73  corresponding to the position of the engaging unit  71 . 
         [0205]    The projecting abutting unit  74  is formed in a round shape so as to correspond to the movement of the rotary operation member  13 . 
         [0206]    The cover member  73  includes a escape unit  75  which avoids the interference between the cover member  73  and the protruded unit  2   c  which is arranged at one of the pillars  2   a.    
         [0207]    This escape unit  75  is formed to have a concave shape at the position on the affixed-side member  4  side surface of the cover member  73  corresponding to the protruded unit  2   c.    
         [0208]    The biasing units  12  bias the engaging units  71  and  71  of the locking member  11  toward the to-be-engaged units  10  side. As shown in  FIGS. 1, 3 and 8 to 12 , coil-like tension springs are used in the embodiment. 
         [0209]    With respect to each tension spring  12 , the two ends thereof are hook units  12   a  and  12   a  which are formed in a hook-like shape. One of the hook units  12   a  and  12   a  is hooked to an engaging unit  71  and the other is hooked to a catch unit  28   b  which is arranged at a lock holding unit  28  of the affixed-side member  4 . The tension springs  12  are respectively arranged between the engaging units  71  and the lock holding units  28 . Further, a plurality of tension sprints  12  are arranged at both of the engaging units  71  and  71  of the locking member  11  and at both of the lock holding units  28  and  28  of the affixed-side member  4 . 
         [0210]    That is, the engaging units  71  and  71  are pulled toward the lock holding units  28  and  28  side by the tension springs  12  and  12 . In such way, the engaging units  71  and  71  are in a state being biased toward the plurality of teeth  60   a  . . . side. 
         [0211]    The biasing units  12  of the embodiment are coil-like tension springs  12  which are arranged between the engaging unit  71  and the lock holding units  28 . However, this is not limitative in any way. For example, as shown in  FIG. 14 , a winding spring  12 A having a tip  12 Ab which extends toward the front surface side from the back surface side of the affixed-side member  4  may be used. 
         [0212]    With respect to such winding springs  12 A, the main bodies  12 Aa are to be arranged on the back surface side of the affixed-side member  4  and are fixed there by being wounded around the to-be-held unit  70 . The tip units  12 Ab go over the side surfaces of the affixed-side member  4  and are hooked to the engaging units  71 . In such way, the engaging units  71  can be engaged with the plurality of teeth  60   a  of the to-be-engaged units  10 . 
         [0213]    The rotary operation member  13  is made of resin. As shown in  FIGS. 1, 3, 4 and 6 , for example, the rotary operation member  13  is held by the movable-side member  5  so as to rotate freely and operates the engaging unit  71  of the locking member  11 . That is, the rotary operation member  13  rotates in the direction to operate the engaging units  71  in the direction which is opposite to the biasing direction of the tension sprints  12  and to release the engaged state with the plurality of teeth  61   a.    
         [0214]    The rotary operation member  13  is arranged in the direction in which the engaging units  71  of the locking member  11  are biased by the tension springs  12 . 
         [0215]    The rotary operation member  13  includes a first operation unit  80 , a second operation unit  81  and a rotary shaft unit  82  which is the rotary shaft. The first operation unit  80 , the second operation unit  81  and the rotary shaft unit  82  are formed integrally. 
         [0216]    The rotary shaft unit  82  is formed in a column shape and is held by the upper abutting unit  33   a  and the lower abutting unit  33   b  of the holding unit  33  abutting the outer circumference surface of the column shape. 
         [0217]    The assembling direction of the rotary operation member  13  to the holding unit  33  is set so as to correspond to the rotary shaft direction of the rotary operation member  13  (that is, the length direction of the rotary shaft unit  82 ). That is, the rotary operation member  13  is configured so as not to be pulled out easily in directions other than the direction which is opposite to the assembling direction (that is, the projection direction of the holding unit  33 ) in a state where the rotary operation member  13  is held by the holding unit  33 . 
         [0218]    The rotary shaft unit  82  is arranged below the front-back locking mechanism and is arranged above the up-down locking mechanism. 
         [0219]    The first operation unit  80  is for operating the front-back locking mechanism. The first operation unit  80  is formed so as to protrude toward the affixed-side member  4  from the part of the outer circumference surface of the rotary shaft unit  82  which is within the range where the upper abutting unit  33   a  and the lower abutting unit  33   b  do not abut each other. The tip of the first operation unit  80  in the protruding direction is arranged below the cover member  73  of the locking member  11  and the upper surface of the first operation unit  80  is in contact with the projecting abutting unit  74 . 
         [0220]    The tip of the first operation unit  80  in the protruding direction is arranged below the rotary shaft unit  82 . Therefore, when the first operation unit  80  is rotated upward with the rotary shaft unit  82  being the shaft, the cover member  73  can be moved upward. 
         [0221]    The rotary operation member  13  includes concave units  83  and  83  in which the tips of the holding units  33  are to be inserted when the rotary operation member  13  rotates. That is, at the boundary part of the first operation unit  80  and the rotary shaft unit  82 , the concave units  83  and  83 , in which the plurality of claw units  33   c  and  33   c  of the upper abutting unit  33   a  of the holding unit  33  are inserted when the rotary operation member  13  rotates, are formed. Therefore, if the rotary operation unit  13  rotates upward, the claw units  33   c  and  33   c  are inserted in the concave units  83  and  83 . Therefore, the rotational moving amount increases for that part. 
         [0222]    The second operation unit  81  is for operating the up-down locking mechanism and is formed so as to project downward from the approximately center in the lower surface of the first operation unit  80 . The tip of the second operation unit  81  in the projecting direction is arranged below the up-down locking member  14  and the approximate center of the second operation unit  81  in the projecting direction is at substantially the same height as the up-down locking member  14 . 
         [0223]    With respect to the surface of the second operation unit  81  on the affixed-side member  4  side, it is parted from the up-down locking member  14  when the up-down locking mechanism is locked and it is in contact with the up-down locking mechanism  14  when the up-down locking mechanism is unlocked. The surface of the second operation unit  81  which is the opposite to the surface on the affixed-side member  4  side is in contact with the button  9  (after mentioned). 
         [0224]    By adapting the above configuration, movement of the movable-side member  5  in the front and back directions with respect to the affixed-side member  4  can be locked or unlocked at any of a plurality of positions, that is, at a position where the engaging unit  71  engages with any of the plurality of teeth  60   a.    
       (Up-Down Locking Mechanism) 
       [0225]    The up-down locking mechanism is provided with respect to the pair of pillars  2   a  and  2   b . The up-down locking mechanism is to lock the affixed-side member  4  at any of the plurality of positions in the up and down directions with respect to the pair of pillars  2   a  and  2   b.    
         [0226]    The up-down locking mechanism includes a plurality of cutouts  15  . . . which are formed in at least one of the pillars  2   a  and  2   b  forming the pair, a pair of pillar holding units  4   a  and  4   b , the up-down locking member  14  and the rotary operation member  13 . 
         [0227]    It is sufficient that the plurality of cutouts  15  are formed in at least one of the pillars  2   a  and  2   b  forming the pair, the one being the pillar to which the up-down locking member  14  is provided. However, since the plurality of cutouts  15  are to be used in the mechanism for preventing the pillars  2   a  and  2   b  from sliding out, the mechanism being configured by the lock units  3   d  and  3   d  of the pair of holder unit  3  and  3 , in the embodiment, the plurality of cutouts  15  . . . are formed in both pillars  2   a  and  2   b  forming the pair. 
         [0228]    As shown in  FIGS. 1, 6 and 10 , the plurality of cutouts  15  are formed in a multiple step manner along the length direction of the pillars  2   a  and  2   b  forming the pair. The plurality of cutouts  15  . . . are formed on the outer circumference surfaces of the pillars  2   a  and  2   b  forming the pair near the centers thereof. 
         [0229]    As described above, the pillar holding units  4   a  and  4   b  forming the pair are for respectively holding the pillars  2   a  and  2   b  forming the pair. In such way, the affixed-side member  4  can move in the up and down directions along the pair of pillars  2   a  and  2   b.    
         [0230]    The up-down moving range of the affixed-side member  4  is based on the range where the projecting units  2   c  and  2   c  provided at the pillars  2   a  and  2   b  forming the pair can slide along the slits  31   f  and  31   f  which are formed on the sides of the affixed-side member  4 . 
         [0231]    The up-down locking member  14  is held by one of the lock holding units  28  and  28  which are respectively formed at the pillar holding units  4   a  and  4   b  forming the pair, the one being the lock holding unit  28  to which the rotary operation member  13  is arranged. 
         [0232]    The up-down locking member  14  includes an engaging unit (not shown) which engages with a cutout  15  inside the lock holding unit  28  and a biasing member (not shown) which biases the engaging unit in the direction engaging with the cutout  15 . 
         [0233]    If the up-down locking member  14  is operated so as to be pushed in to the back of the lock holding unit  28 , the engaging unit, which is not shown, parts from the cutout  15 . If the up-down locking member  14  is not operated as described above, the engaging unit, which is not shown, is to be in the state engaging with the cutout  15 . 
         [0234]    The rotary operation member  13  includes the second operation unit  81  for operating the up-down locking member  14  as described above. On a side surface of the second operating member  81  that abuts the up-down locking member  14 , a groove  84  which engages with the lower end of the up-down locking member  14  when abutting the up-down locking member  14  is formed. 
         [0235]    The first operation unit  80  and the second operation unit  81  are interlinked to rotate. The second operation unit  81  can carry out the unlocking operation by the up-down locking mechanism at the same time when the first operation unit  80  carries out the unlocking operation of the front-back locking mechanism. 
         [0236]    The length of the rotary operation member  13  in the front and back directions is set to be the length according to the moving distance of the movable-side member  5 . That is, the first operation unit  80  is to be abutted by the projecting abutting unit  74  at all parts along its length direction. The second operation unit  81  is to be abutted by the button  9  at all parts along its length direction, and all parts of the second operation unit  81  abut the up-down locking member  14 . The rotary shaft unit  82  is to be held by the holding unit  33  along its length direction. 
         [0237]    Since all parts of the second operation unit  81  along its length direction are abutted by the button  9 , the positional relation between the rotary operation member  13  and the button  9  changes according to moving of the movable-side member  5  in the front and back directions. However, the positional relation between the front cover  30  and the back cover  31  which are the movable-side member  5  and the button  9  does not change. 
         [0238]    By adopting the above described configuration, the affixed-side member  4  can be locked or unlocked at any of the plurality of positions in the up and down directions with respect to the pair of pillars  2   a  and  2   b , that is, at any of the positions where the plurality of cutouts  15  are formed. 
         [0239]    The button  9  which is the operation unit  9  is to be attached to the button attachment unit  34  which is arranged on the sides of the front cover  30  and the back cover  31  as described above, and the button  9  abuts the rotary operation member  13 . By the button  9  being pushed in to the inner space unit, the rotary operation member  13  can be operated. 
         [0240]    The button  9  includes a button main body  90  and a cylindrical unit  91 . 
         [0241]    The button main body  90  is inserted in the cylindrical unit  91  and can freely move forward and backward along the cylindrical unit  91 . The button main body  90  includes a surface unit  90   a  and a protruding unit  90   b.    
         [0242]    The surface unit  90   a  is the part where a person operating the button  9  directly touches. 
         [0243]    The protruding unit  90   b  is arranged at the end part of the button main body  90  on the inner space unit side thereof and is the part that abuts the rotary operation member  13 . In particular, the protruding unit  90   b  abuts the lower end (the end in the projecting direction) of the second operation unit  81  of the rotary operation unit  13 . 
         [0244]    The cylindrical unit  91  is held by being inserted in the button holding unit  34   c  of the button attaching unit  34 . The cylindrical unit  91  includes a plurality of engaging claw units  91   a  which engage with the button holding unit  34   c  when the cylindrical unit  91  is inserted in the button holding unit  34   c.    
         [0245]    By adapting the configuration as described above, the rotary operation member  13  can rotate upward with the rotary shaft unit  82  being the shaft. With this operation, the locking member  11  can be operated by the first operation unit  80  and the up-down locking member  14  can be operated by the second operation unit  81 . 
         [0246]    Next, operation of the headrest  1  having the above described configuration will be described. 
         [0247]    The operation of the headrest  1  includes the operation of the movable-side member  5  moving forward in the direction parting from the affixed-side member  4  and moving backward so as to return from forwardly parted state. Further, the operation of the headrest  1  includes the operation of the affixed-side member  4  including the pair of pillar holding units  4   a  and  4   b  moving in the up and down directions along the pair of pillars  2   a  and  2   b.    
         [0248]    First, operation of the movable-side member  5  will be described. 
         [0249]      FIGS. 8 and 9  show the state where the movable-side member  5  is near the affixed-side member  4 . That is, the movable-side member  5  is in the state returned to the back although not totally to the very back. When the button  9  is not being operated, the engaging unit  71  is in the state engaging with the tooth  60   a  of the to-be-engaged unit  10 , and the moving of the movable-side member  5  in the front and back directions is locked. 
         [0250]    Starting from such state, in order to move the movable-side member  5  so as to part forwardly from the affixed-side member  4 , first, the button  9  is pushed in to make the rotary operation member  13  rotate to the X linkage mechanism side. With such operating, the first operation unit  80  is rotated upward and the engaging unit  71  provided with the cover member  73  is pushed upward. 
         [0251]    In such way, since the engaging units  71  part from the teeth  60   a  of the to-be-engaged units  10 , the locking of the movement of the movable-side member  5  in the front and back directions by the locking member  11  can be unlocked. 
         [0252]    Then, while maintaining the state where the engaging units  71  being pushed up, the movable-side member  5  is moved in the direction parting forwardly from the affixed-side member  4 . 
         [0253]    At this time, the to-be engaged units  10  move forward with the rotary operation of the inner-side link member  6  and the outer-side link member  7 . At this time, the connecting member S of the inner-side link member  6  and the connecting member S of the outer-side link member  7  move upward along the elongated holes  26   a  and the elongated holes  36   a  of the plurality of lower supporting units  26  and  36 . 
         [0254]    When the operating of the button  9  is stopped at a desired position, the engaging units  71  return to the original positions by being biased toward the plurality of teeth  60   a  according to the biasing force of the tension springs  12  and engage with any of the plurality of teeth  60   a . In such way, as shown in  FIGS. 10 and 11 , the movable-side member  5  can be moved to the direction parting forwardly from the affixed-side member  4  to lock the movement of the movable-side member  5  at a desired position. 
         [0255]    At this time, there is a case where the engaging units  71  do not fit in the dents between the teeth  60   a  and  60   a  which are next to each other and come into contact with the tips near the teeth  60   a . In such case, by the movable-side member  5  being moved in either front or back direction without operating the button  9 , the engaging units  71  fall in the nearest dints and the movable-side member  5  can be locked. 
         [0256]    Similarly, when the movable-side member  5  being returned to the back, first, the button  9  is pushed in and the cover member  73  is operated to unlock the locking by the engaging units  71 . 
         [0257]    Thereafter, it is sufficient to return the movable-side member  5  to the back and stop the operation of the button  9  at a desired position. At this time, the X linkage mechanism operates reversely from when the movable-side member  5  is moved to the front. 
         [0258]    As described above, the movable-side member  5  can be moved in the front and back directions and a step-wise position adjustment according to the arrangement of the plurality of teeth  60   a  of the to-be-engaged units  10  can be realized. That is, the position adjustment of the headrest  1  in the front and back directions can be carried out in a step-wise manner. 
         [0259]    Next, upward and downward operation of the affixed-side member  4  including the pair of pillar holding unit  4   a  and  4   b  will be described. 
         [0260]      FIGS. 8 and 9  shows the state where the pair of pillar holding unit  4   a  and  4   b  are positioned at the downward side of the pair of pillars  2   a  and  2   b . When the button  9  is not being operated, the engaging unit of the up-down locking member  14  is in the state being engaged with one cutout  15  at the lower side of the pillar  2   a , and the movement of the pair of pillar holding units  4   a  and  4   b  in the up and down directions is locked. 
         [0261]    Starting from such state, in order to move the pair of pillar holding units  4   a  and  4   b  upward along the pair of pillars  2   a  and  2   b , first, the button  9  is pushed inside to make the rotary operation member  13  rotate toward the X linkage mechanism side. With this operation, the second operation unit  81  is rotated toward the X linkage mechanism side to push in the up-down locking member  14  to the back of the lock holding units  28 , and the engaging units which are not shown are moved to the back of the lock holding units  28 . 
         [0262]    In such way, the engaging unit of the up-down locking member  14  parts from a cutout  15  of the pillar  2   a . Therefore, the locking of the moving of the pair of pillar holding units  4   a  and  4   b  in the up and down directions by the engaging unit of the up-down locking member  14  can be unlocked. 
         [0263]    Then, while maintaining the state where the engaging unit of the up-down locking member  14  is moved to the back of the lock holding unit  28 , the pair of pillar holding units  4   a  and  4   b  is moved upward along the pair of pillars  2   a  and  2   b  and then the affixed-state member  4  is moved upward along the pair of pillars  2   a  and  2   b.    
         [0264]    At this time, the movable-side member  5 , and the X linkage mechanism and the like move upward with the moving of the affixed-side member  4 . 
         [0265]    When the operation of the button  9  is stopped at a desired position, the engaging unit of the up-down locking member  14  returns to the original position due to the biasing force of the biasing member which is not shown, and engages with one cutout  15  at the upper side of the pillar  2   a . In such way, as shown in  FIGS. 10 and 11 , the pair of pillar holding units  4   a  and  4   b  are moved upward along the pair of pillars  2   a  and  2   b  and the movement of the pair of pillar holding units  4   a  and  4   b  can be locked at a desired position. 
         [0266]    At this time, there is a case where the engaging unit of the up-down locking member  14  does not fit in the dent between the cutouts  15  and  15  which are next to each other in the up and down directions and contacts the outer circumference of the pillar  2   a . In such case, by moving the pair of pillar holding unit  4   a  and  4   b  in either up or down direction without operating the button  9 , the engaging unit falls in the nearest cutout  15  and the pair of pillar holding units  4   a  and  4   b  can be locked. 
         [0267]    Similarly, when moving the pair of pillar holding units  4   a  and  4   b  downward, first, the button  9  is pushed in to operate the second operation unit  81  so that the locking by the engaging unit of the up-down locking member  14  is unlocked. 
         [0268]    Thereafter, the pair of pillar holding units  4   a  and  4   b  and the affixed-side member  4  are moved downward and it is sufficient to stop the operation of the button  9  at a desired position. At this time, the movable-side member  5 , the X linkage mechanism and the like also move downward with the moving of the pair of pillar holding units  4   a  and  4   b.    
         [0269]    As described above, the pair of pillar holding units  4   a  and  4   b  can be moved in the up and down directions and a step-wise position adjustment according to the plurality of cutouts  15  . . . of the pillar  2   a  can be realized. That is, the position adjustment of the headrest  1  in the up and down directions can be carried out in a step-wise manner. 
         [0270]    According to the embodiment, the front-back positional adjustment of the movable-side member  5  using the to-be-engaged units  10  and supporting of the heat by the to-be-engaged units  10  at the time collision are compatible. Therefore, the level of comfort and security of the seat when a passenger sits thereon can be improved. 
         [0271]    Since the plurality of to-be-engaged units  10  and  10  are arranged at a plurality of parts having the moving mechanism therebetween, operation of the moving mechanism and the front-back locking mechanism can be carried out in a good balance. Further, since the head can be supported by the plurality of to-be-engaged units  10  and  10 , the level of security can be improved. 
         [0272]    Since the connecting members S are used to connect the to-be-engages units  10 , the link  6  ( 7 ) and the supporting units  35  ( 36 ) and used as rotary shafts, the number of parts needed can be reduced due to sharing the parts. 
         [0273]    Even if the parts to be connected increase, they can be connected by the connecting members S. Therefore, the effect of reduction in the number of parts due to sharing can be improved even more. 
         [0274]    Therefore, such configuration can preferably respond to the request to reduce the number of parts by sharing the parts. 
         [0275]    Moreover, the length in the up and down directions of the part near the upper end of the elongated hole  64   a  of one of the attachment units  64  can be made longer for the part corresponding to the very front teeth  60   a . Therefore, rigidity of one of the attachment units  64  can be improved. 
         [0276]    Therefore, such configuration can preferably respond to the request to improve the rigidity of one of the attachment units  64  and the to-be-engaged units  10 . 
         [0277]    By forming at least one of the plurality of reinforcement units  53  . . . of the link member  7  ( 6 ) in the honeycomb structure, the link member  7  ( 6 ) can be lightened and reinforced so as not to bend easily. 
         [0278]    Therefore, such configuration can preferably respond to the request to make the link member  7  ( 6 ) lighter and to reinforce the link member  7  ( 6 ) so as not to bend easily. 
         [0279]    Interference between the reinforcement rib  37  of the front cover  30  and the front end part of the link member  6  ( 7 ) can be prevented, and rigidity of the front cover  30  can be improved by the reinforcement rib  37 . 
         [0280]    Therefore, such configuration can preferably respond to the request to prevent interference between the reinforcement rib  37  and the front end part of the link member  6  ( 7 ) and to improve rigidity of the front cover  30 . 
         [0281]    The upper end parts of the pair of pillar holding units  4   a  and  4   b  can be connected by the connector  4   d . Therefore, the connecting condition of the pillar holding units  4   a  and  4   b  forming the pair can be improved and rigidity of the affixed-side member  4  can be improved. 
         [0282]    Therefore, such configuration can preferably respond to the request to improve the connecting condition of the pillar holding units  4   a  and  4   b  forming the pair and to improve the rigidity of the affixed-side member  4 . In the technique of Patent Document 1, the back-side fixated rotary shaft which is the rotary shaft of the arms constituting the link member is also used as the member connecting the upper end parts of the left and right side surfaces. Therefore, there has been a desire to improve the rigidity. In view of this, the affixed-side member  4  of the embodiment is preferable since the rigidity is improved by the connector  4   d.    
         [0283]    Since the moving mechanism can be housed in the concave unit  22 , the limited space between the affixed-side member  4  and the movable-side member  5  can be used efficiently, and the headrest  1  can be formed in a compact manner. 
         [0284]    Therefore, such configuration can preferably respond to the request to form the headrest  1  in a compact manner. 
         [0285]    The projecting tips of the to-be-engaged units  10  which are inserted in the through holes  23   a  and  23   b  are held by the affixed-side member  4  in which the through holes  23   a  and  23   b  are formed. Further, since the to-be-engaged units  10  can be supported by the walls  24   a  and  24   b  which face the to-be-engaged units  10 , stability of the movable-side member  5  at the time of front-back positional adjustment can be improved. 
         [0286]    Therefore, such configuration can preferably respond to the request to improve the stability of the movable-side member  5  at the time of front-back positional adjustment. 
       INDUSTRIAL APPLICABILITY 
       [0287]    The headrest of the embodiment can be applied to a headrest which receives the head of a passenger who sits on a seat. 
       REFERENCE SIGN LIST 
       [0000]    
       
           1  headrest 
           2   a  pillar 
           2   b  pillar 
           4  affixed-side member 
           4   a  pillar holding unit 
           4   b  pillar holding unit 
           4   c  back side connector 
           4   d  connector 
           5  movable-side member 
           6  first link member 
           7  second link member 
           8  cross connection unit 
           9  operation unit 
           10  to-be-engaged unit 
           11  locking member 
           12  biasing unit 
           13  rotary operation member 
           14  up-down locking member 
           15  cutout 
           20  pillar inserting hole 
           23   a  through hole 
           23   b  through hole 
           24   a  wall 
           24   b  wall 
           25  supporting unit 
           25   a  through hole 
           26  supporting unit 
           26   a  through hole 
           27  reinforcement unit 
           28  lock holding unit 
           28   a  opening 
           28   b  catch unit 
           30  front cover 
           30   b  surrounding unit 
           31  back cover 
           31   b  surrounding unit 
           33  holding unit 
           35  supporting unit 
           35   a  through hole 
           35   b  protruding unit 
           36  supporting unit 
           36   a  through hole 
           36   b  protruding unit 
           40  first arm 
           41  second arm 
           42  connection 
           50  side wall unit 
           51  inside unit 
           52  connection 
           53  reinforcement unit 
           60  first protruding unit 
           60   a  plurality of teeth 
           61  second protruding unit 
           62  space 
           63  attachment unit 
           63   a  through hole 
           64  attachment unit 
           64   a  through hole 
           70  to-be-held unit 
           71  engaging unit 
           72  connecting unit 
           73  cover member 
           74  protruding abutting unit 
           75  escape unit 
           80  first operation unit 
           81  second operation unit 
           82  rotary shaft unit 
           83  concave unit 
           90  button main body 
           90   b  protruding unit