Abstract:
A disc changer apparatus includes a disc table, reproducing device, a first tray, a second tray, containing device, and movement device. The first tray carries a disc mounted thereon between a loading position at which a disc is loaded and a mounting position at which a disc is mounted on the disc table and between the disc mounting position and a containing position at which a disc is contained. The second tray is engaged with the first tray, to carry the first tray between the disc loading position and the disc mounting position. The containing device stacks and contains the first trays in a stacking direction substantially perpendicular to principal planes of discs mounted on the first trays. The moving device moves at least one of the first trays contained in the containing device in one direction based on the stacking direction, to form a containing space for containing the first tray located at the disc mounting position on the side, opposed to the side of the one direction, of the containing device.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a disc changer apparatus, and particularly to a technical field of a disc changer apparatus for suitably selecting one of a plurality of disc-like recording media inserted in a housing and performing reproduction of information from the selected recording medium and the like. 
     Known disc changer apparatuses have a configuration including trays for carrying disc-like recording media, a stocker having a plurality of containing portions for separately containing the disc-like recording media mounted on the trays, and a drive portion for recording or reproducing information signals on or from a desired one of the disc-like recording media carried by the trays. 
     One of these related art disc changer apparatuses is of a type in which at the time of containing a disc-like recording medium in the stocker, the stocker is lifted or lowered to contain the disc-like recording medium in an empty containing portion. 
     In the above-described related art disc changer apparatus in which the stocker is lifted or lowered to contain a disc-like recording medium in an empty containing portion, it is required to provide a specialized lifting/lowering mechanism, a sensor for detecting an empty containing portion, and the like, and further to provide a specialized motor for operating the lifting/lowering mechanism in addition to a motor for carrying the trays. As a result, there occurs a problem in increasing the number of parts, thereby obstructing the reduction in production cost. 
     On the other hand, there is known a disc changer apparatus intended to reduce the number of parts, which includes a plurality of containing portions for containing disc-like recording media, wherein roulette type trays serving as a stocker are rotated to exchange the disc-like recording media from each other; however, in such a disc changer apparatus, since the disc-like recording media are contained on one plane, there occurs a problem in increasing the entire size of the disc changer apparatus. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to reduce the number of parts of a disc changer apparatus and to miniaturize the disc changer apparatus. 
     To achieve the above object, according to a first aspect of the present invention, there is provided a disc changer apparatus including: 
     a disc table rotating together with a disc mounted thereon; 
     reproducing means for reproducing information from a disc rotating together with the disc table; 
     a first tray for carrying a disc mounted thereon between a loading position at which a disc is loaded and a mounting position at which a disc is mounted on the disc table and between the disc mounting position and a containing position at which a disc is contained; 
     a second tray which is engaged with the first tray for carrying the first tray between the disc loading position and the disc mounting position; 
     containing means for stacking and containing a plurality of the first trays in a stacking direction substantially perpendicular to principal planes of discs mounted on the first trays; and 
     moving means for moving at least one of the first trays contained in the containing means in one direction based on the stacking direction, to form a containing space for containing the first tray located at the disc mounting position on the side, opposed to the side of the one direction, of the containing means. 
     With this configuration, unlike the related art disc changer apparatus in which the stocker is lifted/lowered to contain a tray in an empty containing portion, it is possible to eliminate the need of provision of a specialized lifting/lowering mechanism, a sensor for detecting an empty containing portion, and the like, and hence to correspondingly reduce the number of parts. This is advantageous in reducing the production cost. 
     Since the sub-trays can be stacked in the stocker without use of roulette type trays serving as the stocker in consideration of reduction in the number of parts, the disc changer apparatus can be miniaturized. 
     According to a second aspect of the present invention, there is provided a disc changer apparatus including: 
     a base unit including a disc table rotating together with a disc mounted thereon and reproducing means for reproducing information from a disc rotating together with the disc table; 
     a sub-tray for carrying a disc mounted thereon between a loading position at which a disc is loaded and a mounting position at which a disc is mounted on the disc table and between the disc mounting position and a containing position at which a disc is contained; 
     a main tray which is engaged with the sub-tray for carrying the sub-tray between the disc loading position and the disc mounting position; 
     a stocker lifted or lowered relative to the main tray, the stocker internally having a plurality of containing portions allowed to stack a plurality of the sub-trays in the lifting/lowering direction of the stocker; 
     a cam gear rotated by a drive motor; 
     a first slider which is moved, along with rotation of the cam gear, in a carrying direction where the sub-trays are carried so as to carry the main tray and the sub-trays in the carrying direction along with movement of the first slider in the carrying direction; 
     a second slider having a cam groove formed into a stepped shape in the lifting/lowering direction of the stocker, wherein the second slider is moved in the carrying direction along with rotation of the cam gear so as to control lifting/lowering operations of at least the base unit and the stocker by the cam groove formed in the second slider; and 
     movement means which is lifted or lowered together with the base unit along with movement of the second slider so as to move at least one of the sub-trays contained in the stocker in the lifting or lowering direction to form one containing portion for containing the sub-tray located at the disc mounting position on the side, opposed to the side of the lifting or lowering direction, of the plurality of containing portions. 
     With this configuration, since the first slider and the second slider are selectively moved in the longitudinal direction by rotation of the cam gear rotated by a motor to move the main tray and the sub-trays and lift or lower the base unit and the stocker, it is possible to more reduce the number of parts. 
     In the disc changer apparatus according to the second aspect, preferably, the cam gear has a cam groove in one surface and an engagement pin on the other surface; the first slider has a cam groove in which the engagement pin of the cam gear is to be engaged; and the cam groove of the first slider has a first projection for moving, when the sub-tray is moved from the disc containing position to the disc mounting position, the first slider to a first position corresponding to the disc mounting position, and a second projection for moving, when the sub-tray is moved from the disc loading position to the disc mounting position, the first slider to a second position offset to the disc containing position side from the first position corresponding to the disc mounting position. 
     With this configuration, when the sub-tray is moved from the disc containing position to the disc mounting position, the engagement pin of the cam gear is moved in the movement direction from the disc containing position to the disc mounting position by an amount corresponding to the projecting amount of the first projection, while when the main tray is moved from the pull-out position to the disc mounting position, the engagement pin of the cam gear is moved in the movement direction from the pull-out position to the disc mounting position by an amount corresponding to the projecting amount of the second projection. As a result, it is possible to certainly move the sub-tray and the main tray to the disc mounting position. 
     The disc changer apparatus according to the second aspect, preferably, further includes a housing provided to cover the components of the disc changer apparatus; a control circuit board provided in the housing and having at least a control circuit for controlling the motor; a relay board provided in the housing and electrically connected to the control circuit board via a flexible board; and a main board provided in the housing, the main board being electrically connected to the relay board via a flexible board so as to control at least power supply to the control circuit board via the relay board. 
     With this configuration, since a vibration system generated at the time of reproducing the disc-like recording medium and the like is ended in the disc changer apparatus and is less affected by another connection line led from the relay board and connected to the main board, it is possible to reduce occurrence of tracking errors and hence to optimize the operation of reproducing signals recorded on a disc-like recording medium and the like. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings showing an embodiment of a disc changer apparatus of the present invention, in which FIGS. 1 to  44  are for illustrating the configuration of the disc changer apparatus and FIGS. 45 to  73  are for illustrating the operation of the disc changer apparatus, wherein: 
     FIG. 1 is a schematic front view of acoustic equipment provided with a disc changer apparatus; 
     FIG. 2 is a plan view of a housing of the disc changer apparatus; 
     FIG. 3 is a plan view showing the housing in which a cover body, a unit holder, and the like are arranged; 
     FIG. 4 is a plan view of a main tray; 
     FIG. 5 is a rear view of the main tray; 
     FIG. 6 is a plan view showing a state in which the main tray is connected to a sub-tray; 
     FIG. 7 is a plan view showing another state in which the main tray is connected to the sub-tray; 
     FIG. 8 is a side view of the main tray; 
     FIG. 9 is an enlarged perspective view of a lock lever; 
     FIG. 10 is a plan view of a rack member; 
     FIG. 11 is a side view of the rack member; 
     FIG. 12 is an enlarged plan view of the sub-tray; 
     FIG. 13 is an enlarged bottom view of the sub-tray; 
     FIG. 14 is an enlarged plan view showing the unit holder on which a base unit is arranged; 
     FIG. 15 is an enlarged side view showing the unit holder on which the base unit is arranged; 
     FIG. 16 is an enlarged sectional view showing the unit holder on which the base unit is arranged; 
     FIG. 17 is an enlarged plan view showing a chucking member on which a chucking pulley is supported; 
     FIG. 18 is an enlarged sectional view showing the chucking member on which the chucking pulley is supported; 
     FIG. 19 is an enlarged plan view of a stocker; 
     FIG. 20 is an enlarged bottom view of the stocker; 
     FIG. 21 is an enlarged side view of the stocker; 
     FIG. 22 is an enlarged perspective view of a restricting member; 
     FIG. 23 is an enlarged rear view, with parts partially cutaway, showing a state before the sub-tray is lifted up; 
     FIG. 24 is an enlarged rear view, with parts partially cutaway, showing a state that the sub-tray is lifted up; 
     FIG. 25 is an enlarged right side view of a hold-down member; 
     FIG. 26 is an enlarged rear view of the hold-down member; 
     FIG. 27 is an enlarged left side view of the hold-down member; 
     FIG. 28 is an enlarged side view showing the inner surface of a lifting/lowering slider; 
     FIG. 29 is an enlarged side view showing the outer surface of the lifting/lowering slider; 
     FIG. 30 is an enlarged side view of a lock releasing lever; 
     FIG. 31 is a plan view showing a main mechanism arranged on the housing; 
     FIG. 32 is a schematic enlarged plan view showing the main mechanism; 
     FIG. 33 is a schematic enlarged plan view showing another main mechanism; 
     FIG. 34 is an enlarged plan view of a drive force transmission slider; 
     FIG. 35 is an enlarged bottom view of the drive force transmission slider; 
     FIG. 36 is an enlarged plan view of a cam gear; 
     FIG. 37 is an enlarged bottom view of the cam gear; 
     FIG. 38 is an enlarged plan view of the slider for movement; 
     FIG. 39 is an enlarged bottom view of the slider for movement; 
     FIG. 40 is an enlarged side view of a drive rack; 
     FIG. 41 is an enlarged plan view of the drive rack; 
     FIG. 42 is a side view showing a mechanism arranged on a side surface of the housing; 
     FIG. 43 is an enlarged bottom view showing a control circuit board and a relay board; 
     FIG. 44 is an enlarged front view of a rear surface panel; 
     FIG. 45 is a side view showing a state (initial state) that the main tray is located at a pull-out position; 
     FIG. 46 is a side view, with parts partially cutaway, showing initial states of the unit holder on which the base unit is arranged and the chucking member for supporting the chucking pulley; 
     FIG. 47 is a side view showing initial states of the chucking member for supporting the chucking pulley and the stocker; 
     FIG. 48 is an enlarged plan view showing initial states of the cam gear and the like; 
     FIG. 49 is a side view showing a state that the main tray is located at a disc mounting position; 
     FIG. 50 is an enlarged plan view showing states of the cam gear and the like when the main tray is located at the disc mounting position and the unit holder is located at a lower position; 
     FIG. 51 is a side view showing a state that the main tray is located at the disc mounting position and the unit holder is halfway through lifting; 
     FIG. 52 is a side view showing states of the chucking member and the like when the disc-like recording medium is chucked; 
     FIG. 53 is a side view, with parts partially cutaway, showing the states of the unit holder and the like when the disc-like recording medium is chucked; 
     FIG. 54 is an enlarged side view, with parts partially cutaway, showing a state that the unit holder is positioned to the sub-tray; 
     FIG. 55 is an enlarged plan view showing states of the cam gear and the like when information is reproduced from the disc-like recording medium; 
     FIG. 56 is a side view showing a state that the chucking of the disc-like recording medium is released; 
     FIG. 57 is an enlarged plan view showing states of the cam gear and the like when the chucking of the disc-like recording medium is released; 
     FIG. 58 is an enlarged side view, with parts partially cutaway, showing a state that the locking of the sub-tray is released; 
     FIG. 59 is a side view showing a state that the sub-tray is contained in the stocker; 
     FIG. 60 is a side view showing a position of the stocker and the like when the sub-trays are contained in the stocker; 
     FIG. 61 is an enlarged plan view showing states of the cam gear and the like when the sub-trays are contained in the stocker; 
     FIG. 62 is an enlarged plan view showing states of the cam gear and the like when the stocker is located at an intermediate position; 
     FIG. 63 is a side view showing a state that the stocker is lowered to the intermediate position; 
     FIG. 64 is a side view showing a state that the sub-tray is pulled out of a second containing portion; 
     FIG. 65 is an enlarged plan view showing states of the cam gear and the like when the sub-tray is pulled out of the second containing portion; 
     FIG. 66 is an enlarged plan view showing states of the cam gear and the like when the stocker is lowered to the lower end; 
     FIG. 67 is a side view showing a state that the stocker is lowered to the lower end; 
     FIG. 68 is a side view, with parts partially cutaway, showing a state that the unit holder is tilted when the stocker is lowered to the lower end; 
     FIG. 69 is a side view showing a state that the sub-tray is pulled out of a first containing portion; 
     FIG. 70 is an enlarged plan view showing states of the cam gear and the like when the sub-tray is pulled out of the first containing portion; 
     FIG. 71 is a side view, with parts partially cutaway, showing a state that the sub-tray contained in the stocker is lifted up; 
     FIG. 72 is a conceptual view showing a state that one of gear teeth of a second side surface gear is in contact with the corresponding one of one-sided wall planes of rack teeth of a rack portion for illustrating backlash between the rack portion and the second side surface gear; 
     FIG. 73 is a conceptual view, similar to FIG. 72, showing a state that one of gear teeth of the second side surface gear is in contact with the corresponding one of the other sided wall planes of the rack teeth of the rack portion; 
     FIG. 74 is a graph showing an experimental example for examining an occurrence state of tracking errors in the case where a control circuit board is connected to a main board via a relay board, wherein values measured at an inner peripheral portion of a disc-like recording medium are shown; 
     FIG. 75 is a graph showing an experimental example for examining an occurrence state of tracking errors in the case where the control circuit board provided in the disc changer apparatus is connected to the main board provided outside the disc changer apparatus not via the relay board, wherein values measured at the inner peripheral portion of the disc-like recording medium are shown; 
     FIG. 76 is a graph, similar to FIG. 74, wherein values measured at an intermediate portion between the inner peripheral portion and an outer peripheral portion of the disc-like recording medium are shown; and 
     FIG. 77 is a graph, similar to FIG. 75, wherein values measured at an intermediate portion between the inner peripheral portion and an outer peripheral portion of the disc-like recording medium are shown. 
    
    
     DESCRIPTION OF THE INVENTION 
     Hereinafter, embodiments of a disc changer apparatus of the present invention will be described with reference to the accompanying drawings. 
     Referring to FIG. 1, there is shown acoustic equipment  100  including, in an outer housing  101 , a disc changer apparatus  1  and the other necessary units. Concretely, a front panel  102  of the outer housing  101  has a liquid crystal display unit  103  located on the upper end side and the disc changer apparatus  1  located on the lower end side; a plurality of operating buttons  104 ; and a slot  105  allowing a disc-like recording medium having a diameter of about 64 mm (Minidisc, trade name) to be inserted in the acoustic equipment  100  therethrough in order to record or reproduce information signals on or from the recording medium. The acoustic equipment  100  also has a radio unit. 
     The disc changer apparatus  1  has necessary members and mechanism in a housing  2  as shown in FIGS. 2 and 3. 
     The housing  2  formed into a vertically-elongated shape has a front surface portion  3  and both side surface portions  4  extending rearward from both side edges of the front surface portion  3  (see FIGS.  2  and  42 ). The side surface portions  4  are each formed into an approximately rectangular shape extending longer in the longitudinal direction. Rear half portions of the side surface portions  4  are connected to each other by an arrangement plate portion  5 . The upper surface of each side surface portion  4  has a slightly wide width in the lateral direction, and has a guide projection  4   a  extending in the longitudinal direction. The inner surface of each side surface portion  4  has, at a position slightly offset from a central portion in the longitudinal direction, a lever supporting pin  4   b  projecting inward therefrom. The inner surface of each side surface portion  4  also has, at a position slightly offset from the central portion in the longitudinal direction, a guide projection  4   c  projecting inward therefrom. The outer surface of each side surface portion  4  has, at a position near the lower end, a guide rail  4   d  extending in the longitudinal direction (see FIG.  42 ). 
     The arrangement plate portion  5  is formed as a flat-plate like gear arrangement portion  5   a  except for right and left end portions of the arrangement plate portion  5 . Both right and left sides of the gear arrangement portion  5   a  are formed into two slider arrangement groove portions  5   b  opened upward. The slider arrangement groove portions  5   b  each extend to the front end portion of the housing  2  (see FIG.  2 ). The back surface of the bottom surface portion forming each slider arrangement groove portion  5   b  has a guide rail  5   c  extending to a position near the front end of the side surface portion  4  (see FIG.  43 ). 
     The arrangement plate portion  5  has a motor shaft insertion hole  5   d  located at a rear end portion, a first gear insertion hole  5   e  located at a central portion, and a second gear insertion hole  5   f  located at a position near the rear end. The arrangement plate portion  5  also has, at a central portion of the back surface, a guide projection  5   g  extending in the longitudinal direction (see FIG.  33 ). 
     A portion on the front side of the gear arrangement portion  5   a  is formed as a stepped portion  6  higher than the gear arrangement portion  5   a . The stepped portion  6  has, on both right and left side edges, two supporting grooves  6   a  extending in the vertical direction (see FIG.  2 ). The housing  2  has a large arrangement space  2   a  located in front of the arrangement plate portion  5 . 
     The front half portion of the housing  2  is covered with a cover body  7  (see FIG.  3 ). The cover body  7  made from a transparent material has, at a central portion, a pulley insertion hole  7   a . The upper surface of the cover body  7  has, at two positions near the rear ends of right and left end portions, two supporting groove portions  7   b.    
     A main tray  8  is longitudinally movably supported on the housing  2  (see FIG.  3 ). The main tray  8  has a receiving surface portion  9 , a front end portion  10  erected from the front end of the receiving surface portion  9 , two side portions  11  erected from both side edges of the receiving portion  9 , and two hold-down portions  12  projecting from the upper edges of the side portions  11  in the direction where the hold-down portions  12  become closer to each other (see FIGS. 4 to  8 ). Both the side edges of the front end portion  10  are continuous to the front edges of the side portions  11  and right end left end portions of the upper edge of the front end portion  10  are continuous to the front edges of the hold-down portions  12 , to form two insertion portions  13  opened inward and rearward on the right and left sides of the main tray  8 . 
     The receiving surface portion  9  includes a base portion  9   a  which is continuous to the front end portion  10  and is formed into an approximately rectangular shape laterally elongated, and two projections  9   b  projecting rearward from right and left ends of the base portion  9   a . The base portion  9   a  has, at both right and left end portions, two positioning holes  9   c  extending longer in the longitudinal direction. Each projection  9   b  has, at a rear end portion, a lock lever arrangement hole  9   d . The receiving surface portion  9  has, at a central portion in the lateral direction, a through-hole  9   e . The receiving surface portion  9  also has, on its back surface, two projecting pieces  9   f  to be restricted (see FIG.  5 ). As shown in FIG. 5, the projecting pieces  9   f  are positioned directly at the back of the lock lever arrangement holes  9   d.    
     Each hold-down portion  12  has a positioning hole  12   a  formed directly over the positioning hole  9   c . The length of the positioning hole  12   a  in the longitudinal direction is shorter than the length of the positioning hole  9   c  in the longitudinal direction. 
     The main tray  8  also has two leg portions  14  projecting rearward from the rear edges of both the side portions  11 . Each leg portion  14  has, at the lower edge of an outer surface portion, a rack portion  14   a  (see FIGS.  5  and  8 ). A portion, continuous to the side portion  11 , of the leg portion  14  is notched so as to be opened outward, which portion is taken as a notch portion  14   b  with no rack portion  14   a  (see FIGS.  5  and  8 ). 
     The main tray  8  has, in portions positioned directly inward from the rack portions  14   a , two sliding grooves  8   a  which are open downward and extend in the longitudinal direction. Each sliding groove  8   a  extends from a front end portion of the side portion  11  to a rear end portion of the leg portion  14  (see FIG.  5 ). The main tray  8  also has, in portions positioned directly inward from the sliding grooves  8   a , grooves  8   b  to be supported which are opened downward and extend in the longitudinal direction. 
     A lock lever  15  is turnably supported in each of the lock lever arrangement holes  9   d  of the main tray  8  (see FIGS. 4,  7  and  9 ). Referring to FIG. 9, the lock lever  15  integrally includes a supporting shaft portion  15   a  extending longer in the lateral direction, an extending portion  15   b  projecting approximately forward from the supporting shaft portion  15   a , and a portion  15   c  to be operated which projects approximately rearward from the supporting shaft portion  15   a . The lock lever  15  further includes a lock projection  15   d  disposed at a front end portion of the extending portion  15   b  in such a manner as to project upward therefrom, two turning restricting projections  15   e  disposed at the front end portion of the extending portion  15   b  in such a manner as to project therefrom in the lateral direction, and a spring receiving projection  15   f  disposed at a position, near the supporting shaft portion  15   a , of the extending portion  15   b.    
     Each lock lever  15  is supported in the lock lever arrangement hole  9   d  in such a manner that the supporting shaft portion  15   a  is turnably supported by part of the opening edge of the lock lever arrangement hole  9   d  and the lock projection  15   d  is biased by a torsion coil spring  16  in the direction where the lock projection  15   d  is moved up. The torsion coil spring  16  is arranged such that a coil portion thereof is wound around the supporting shaft portion  15   a ; one end portion thereof is brought into elastic-contact with the spring receiving projection  15   f ; and the other end portion thereof is brought into elastic-contact with the back surface of the receiving surface portion  9  of the main tray  8 . With this arrangement of the torsion coil spring  16 , since the turning restricting projections  15   e  are brought into elastic-contact with the back surface of the receiving surface portion  9 , the turning of the lock lever  15  in the direction where the lock projection  15   d  is moved up is restricted. 
     Two rack members  17  are movably supported in the sliding grooves  8   a  of the main tray  8  (see FIGS. 8,  10  and  11 ). Referring to FIGS. 10 and 11, each rack member  17  integrally includes a plate-like main portion  17   a  extending longer in the longitudinal direction, a projection  17   b  projecting inward from a front end portion of the main portion  17   a , and a connecting portion  17   c  provided at the leading end of the projection  17   b . The lower edge of the main portion  17   a , which is provided with a rack, is taken as a rack portion  17   d.    
     The main portion  17   a  of each rack member  17  is inserted in and supported by the sliding groove  8   a , and the connecting portion  17   c  thereof is insertable in a connecting groove  18   c  of a sub-tray  18  (which will be described later). 
     The grooves  8   b  to be supported of the main tray  8  are slidably supported by the guide projections  4   a  provided on the upper surfaces of the side surface portions  4  of the housing  2 , whereby the main tray  8  becomes movable in the longitudinal direction. 
     The sub-tray  18 , on which a disc-like recording medium is to be mounted, includes a first mounting recess  18   a  on which a disc-like recording medium having a diameter of about 12 cm is to be mounted, and a second mounting recess  18   b , deeper than the first mounting recess  18   a , on which a disc-like recording medium having a diameter of about 8 cm is to be mounted (see FIGS. 6,  7 ,  12  and  13 ) The sub-tray  18  has a large insertion notch  19  extending inward from the rear end of the sub-tray  18  to a central portion of the mounting recess  18   b.    
     The sub-tray  18  has, at right and left side edges on the front end side, two connecting grooves  18   c  opened outward and has, at right and left side edge portions on the front end side, two positioning holes  18   d . The length of the positioning hole  18   d  in the longitudinal direction is the same as the length of the positioning hole  9   c  of the main tray  8 . The back surface of the sub-tray  18  has, at right and left end portions on the rear end side, two locking recesses  18   e . The sub-tray  18  also has, at a position near the front end of the second mounting recess  18   b , a through-hole  18   f.    
     The disc changer apparatus  1  is provided with three pieces of the sub-trays  18 , which are taken as sub-trays  18 A,  18 B and  18 C (see FIGS. 12 and 13) Each of the sub-trays  18 A,  18 B and  18 C has a light shielding projecting piece  18   g ,  18   h  or  18   i . These sub-trays  18 A,  18 B and  18 C are identical to each other in shape and size except for formation position of the light shielding projecting piece. To be more specific, the sub-tray  18 A has the light-shielding projecting piece  18   g ; the sub-tray  18 B has the light-shielding projecting piece  18   h ; and the sub-tray  18 C has the light shielding projecting piece  18   i.    
     The connecting portions  17   c  of the rack members  17  are inserted in the connecting grooves  18   c  of the sub-tray  18 , whereby the sub-tray  18  is connected to the rack members  17  (see FIG.  6 ). In this state, both right and left side edges of the sub-tray  18  are positioned in the insertion portions  13  of the main tray  8 , so that the sub-tray  18  is movable relative to the main tray  8  in the longitudinal direction along with the movement of the rack members  17  in the longitudinal direction. 
     In a state in which the sub-tray  18  is positioned at the front end of a range movable relative to the main tray  8 , the locking projections  15   d  of the lock levers  15  supported by the main tray  8  are inserted in and engaged with the locking recesses  18   e  of the sub-tray  18 , whereby the sub-tray  18  is locked with the main tray  8 . Accordingly, in such a locking state, the sub-tray  18  is movable in the longitudinal direction together with the main tray  8 , and when the locking of the sub-stray  18  with the main tray  8  is released, the sub-tray  18  is singly movable in the longitudinal direction. In the state that the sub-tray  18  is locked with the main tray  8 , the positioning holes  18   d  of the sub-tray  18  are positioned between the upper and lower positioning holes  12   a  and  9   c  provided in the main tray  8 , and the through-hole  18   f  of the sub-tray  18  is aligned to the through-hole  9   e  of the main tray  8  in the vertical direction (see FIG.  7 ). 
     A unit holder  20  is arranged in the arrangement space  2   a  of the housing  2  (see FIGS. 14 to  16 ). The unit holder  20  integrally includes an arrangement portion  21  formed into a box-like shape opened downward, a projecting portion  22  projecting continuously from the rear edge of the arrangement portion  21 , and two lift-up portions  23  projecting rearward from both right and left ends of the projecting portion  22 . The arrangement portion  21  has, on each of both right and left side surfaces, a pin  21   a  to be supported which is located on the front side and a pin  21   b  to be supported which is located on the rear side. The upper surface of the arrangement portion  21  has a large opening  21   c.    
     The arrangement portion  21  has two positioning projections  21   d  at the right and left ends of a portion near the front end; two positioning projections  21   e  on the right and left end sides of a rear end portion; and two positioning projections  21   f  at the right and left ends of a portion near the rear end. The upper surface of each of the positioning projections  21   d ,  21   e  and  21   f  is tilted (see FIGS.  15  and  16 ). 
     The unit holder  20  has, at a central area of a front end portion in the lateral direction, an optical sensor  20   a  (see FIG.  14 ). 
     The arrangement portion  21  is provided with a base unit  24  which is supported by the unit holder  20  via a damper (not shown). The base unit  24  includes a supporting plate  25 , an optical pickup  26  supported on the supporting plate  25 , a spindle motor  27  fixed on the back surface side of the supporting plate  25 , and a disc table  28  fixed at an upper end portion of a motor shaft of the spindle motor  27  (see FIGS. 14 to  16 ). An annular magnet  28   a  is buried in the disc table  28  (see FIG.  14 ). 
     The optical pickup  26  includes a movable base  26   a  and a biaxial actuator  26   b  disposed on the movable base  26   a . The optical pickup  26  is movable while being guided between a guide shaft  29  and a guide projecting edge  30  positioned in parallel to the guide shaft  29 . The optical pickup  26  and the disc table  28  project upward from an opening  21   c  of the unit holder  20  (see FIGS.  15  and  16 ). 
     A chucking member  31  integrally includes a base portion  32 , a pulley supporting portion  33  provided on the front end side of the base portion  32 , and two leg portions  34  to be operated which project rearward from both right and left end portions of the base portion  32  (see FIGS.  17  and  18 ). 
     The base portion  32  has, on both right and left side surfaces, two shafts  32   a  to be supported which are located at positions near the rear end of the base portion  32  in such a manner as to project outward therefrom. The pulley supporting portion  33  is formed into a disc shape having at its center a pulley supporting hole  33   a . A rear end portion of each leg portion  34  to be operated is formed as a portion  34   a  to be held down. 
     A chucking pulley  35  is formed by mounting a pulley  36  on a disc-like mounting plate  36   a  (see FIGS,  17  and  18 ). The pulley  36  integrally includes a shaft portion  37  and a plurality of hold-down pieces  38  projecting radially from the lower edge of the shaft portion  37 . An annular rubber  39  is stuck on the back surfaces of the hold-down pieces  38 . An iron plate  40  is disposed in the shaft portion  37 . 
     The upper edge of the shaft portion  37  of the pulley  36  is mounted on the mounting plate  36   a , and the shaft portion  37  is inserted in the pulley supporting hole  33   a  of the chucking member  31 , whereby the chucking pulley  35  is supported by the chucking member  31 . In the state in which the chucking pulley  35  is supported by the chucking member  31 , the chucking pulley  35  is movable relative to the chucking member  31  in the axial direction of the shaft portion  37 . 
     The chucking member  31 , which has supported the chucking pulley  35  as described above, is supported by the cover body  7  by inserting the shafts  32   a  to be supported in the supporting groove portions  7   b  of the cover body  7 . In this state, the chucking member  31  is turnable around the shafts  32   a  to be supported. In the state that the chucking member  31  is supported by the cover body  7 , when the portions  34   a  to be held down are not held down from above by hold-down members (which will be described later), the chucking member  31  is turned by its dead weight in the direction where the chucking pulley  35  supported by the chucking member  31  is moved down. When the chucking member  31  is thus turned with its front side directed downward, the chucking pulley  35  is inserted in the cover body  7  through the pulley insertion hole  7   a  of the cover body  7 . 
     A stocker  41  integrally includes an upper wall portion  42  and two side wall portions  43  suspended from both right and left side edges of the upper wall portion  42  (see FIGS. 19 to  21 ). 
     The outer surface of each side wall portion  43  has, in a front end portion, two vertical guide grooves  43   a  spaced from each other in the longitudinal direction, and a vertical groove  43   b  to be guided which is positioned directly rearward from the guide grooves  43   a . The side wall portion  43  has, at positions near the front end, two supporting holes  44  and  45  spaced from each other in the longitudinal direction, and also has, at positions near the rear end, two supporting holes  44  and  45  spaced from each other in the longitudinal direction (see FIG.  21 ). 
     The supporting holes  44  and  45  are formed into shapes similar to each other. The supporting holes  44  are located at the same height, and the supporting holes  45  are higher than the supporting holes  44 . The supporting holes  44  and  45  are each formed into an approximately inverse T-shape. To be more specific, the supporting hole  44  includes a vertical portion  44   a  extending in the vertical direction, and a horizontal portion  44   b  located on the lower side of the vertical portion  44   a  and extending in the longitudinal direction; and the supporting holes  45  includes a vertical portion  45   a  extending in the vertical direction, and a horizontal portion  45   b  located on the lower side of the vertical portion  45   a  and extending in the longitudinal direction. 
     The side wall portion  43  has, on the inner surface of the lower edge, a pin  43   c  to be supported which is located on the front side and a pin  43   d  to be supported which is located on the rear side (see FIG.  20 ). The side wall portion  43  also has, on the inner wall, a pair of slip-off preventive projecting ribs  46  which extend in the longitudinal direction while being spaced from each other in the longitudinal direction. The slip-off preventive projecting pieces  46  are disposed at a height corresponding to the height of a lower side opening edge of the horizontal portion  44   b  of the lower side supporting hole  44 . 
     The guide projections  4   c  provided on the housing  2  are engaged in the grooves  43   b  to be guided, whereby the stocker  41  is supported by the housing  2  in such a manner as to be movable in the vertical direction. 
     Two hold-down members  47  are vertically movably supported by the guide grooves  43   a  provided in each of the side wall portions  43  of the stocker  41  (see FIGS. 25 to  27 ). The hold-down member  47  has a vertically-elongated portion  48  to be supported, and an arm  49  projecting forward from an approximately central portion in the vertical direction of the portion  48  to be supported. A hold-down piece  48   a  projecting outward is provided on the upper edge of the portion  48  to be supported, and a shaft portion  48   b  projecting inward is provided on a lower end portion of the portion  48  to be supported. A plurality of thin pieces  48   c  to be supported are formed on both the front and rear side edges of the portion  48  to be supported. The front end of the arm  49  has a movement restricting projection  49   a  projecting inward. 
     The pieces  48   c  to be supported of the hold-down members  47  are inserted in and supported by the guide grooves  43   a  of each of the side wall portions  43  of the stocker  41 , whereby the hold-down members  47  are vertically movably supported by each of the side wall portions  43  of the stocker  41 . 
     A restricting member  50  is inserted in and turnably supported by each of the supporting holes  44  and  45  (see FIGS. 21 to  24 ). 
     The restricting member  50  integrally includes a shaft portion  50   a  to be supported, a first turning restricting portion  50   b  projecting downward from the shaft portion  50   a  to be supported, a spring receiving portion  50   c  projecting upward from the shaft portion  50   a  to be supported, a restricting projecting portion  50   d  projecting inward from an upper end portion of the spring receiving portion  50   c , and two second turning restricting portions  50   e  projecting forward and rearward from a position near the upper end of the spring receiving portion  50   c  (see FIG.  22 ). The restricting projection  50   d  has a horizontal upper surface  50   f , and an obtusely curved surface  50   g  continuously extending downward, outward from the upper surface  50   f.    
     The restricting member  50  is arranged in the horizontal hole  44  ( 45 ) such that the shaft portion  50   a  to be supported is supported by the horizontal portion  44   b  ( 45   b ) of the horizontal hole  44  ( 45 ), while the first turning restricting portion  50   b  is in contact with the lower opening edge of the inner surface of the horizontal portion  44   b  ( 45   b ) and the second turning restricting portion  50   e  is in contact with the opening side edge of the outer surface of the vertical portion  44   a  ( 45   a ). A biasing member  51  is then mounted to a upper side of the supporting hole  44  ( 45 ) (see FIG.  21 ). 
     The biasing member  51  is composed of a plate spring integrally including a base end portion  51   a , a first spring portion  51   b  suspended from a front end portion of the base end portion  51   a , and a second spring portion  51   c  suspended from a rear end portion of the base end portion  51   a . The biasing member  51  is mounted to the stocker  41  such that the base end portion  51   a  is mounted to the upper sides of the supporting holes  44  and  45 ; the first spring portion  51   b  is brought, from external, into elastic-contact with the spring receiving portion  50   c  of the restricting member  50  supported by the supporting hole  44 ; and the second spring portion  51   c  is brought, from external, into contact with the spring receiving portion  50   c  of the restricting member  50  supported by the supporting hole  45 . As a result, the biasing member  51  gives the restricting member  50  a biasing force acting in the direction where the restricting projection  50   d  projects inward. 
     In the state that the restricting members  50  are supported by the stocker  41  and the biasing members  51  are mounted on the stocker  41  as described above, the sub-tray  18  can be contained in the stocker  41 . An upper space, which is formed between the upper wall portion  42  of the stocker  41  and the four restricting projections  50   d  of the four restricting members  50  supported by the four supporting holes  45  provided in both the side wall portions  43  of the stocker  41 , is taken as a first containing portion  41   a ; An intermediate space, which is formed between the above four restricting projections  50   d  of the four restricting members  50  supported by the four supporting holes  45  provided in both the side wall portions  43  of the stoker  41  and the four restricting projections  50   d  of the four restricting members  50  supported by the four supporting holes  44  provided in both the side wall portions  43  of the stocker  41 , is taken as a second containing portion  41   b . A lower space, which is formed between the above four restricting projections  50   d  of the four restricting members  50  supported by the four supporting holes  44  provided in both the side wall portions  43  of the stocker  41  and the four slip-off preventive projecting ribs  46  provided on both the side wall portions  41  of the stocker  41 , is taken as a third containing portion  41   c  (see FIGS.  23  and  24 ). In addition, the third containing portion  41   c  functions as an insertion area in which the sub-tray  18  is inserted from a disc mounting position. 
     Each of the sub-trays  18 A,  18 B and  18 C is contained in either of the containing portions  41   a ,  41   b  and  41   c  by inserting the sub-tray  18 , from the front side, in the stocker  41 . If the sub-tray  18  is contained in the first or second containing portion  41   a  or  41   b , it is placed on and held by the restricting projections  50   d  of the restricting members  50  (see FIGS.  23  and  24 ), and if the sub-tray  18  is contained in the third containing portion  41   c , it is placed on and held by the slip-off preventive projecting ribs  46  (see FIG.  23 ). 
     If one sub-tray  18  is held in the third containing portion  41   c  and any of the other sub-trays  18  is not held in the first or second containing portion  41   a  or  41   b , the sub-tray  18  held in the third containing portion  41   c  is lifted up and contained in the second containing portion  41   b  by the lift-up portions  23  of the unit holder  20  at the time of upward movement of the unit holder  20  to be described later (see FIGS.  23  and  24 ). 
     Since the sub-tray  18  contained in the third containing portion  41   c  is lifted up by the lift-up portions  23  of the unit holder  20  at the time of upward movement of the base unit  24  (unit holder  20 ) as described above, the base unit  24  (unit holder  20 ) functions as moving means for lifting up the sub-tray  18 . 
     The back surface of the sub-tray  18  is pushed up by the lift-up portions  23 . At this time, both the side edges of the sub-tray  18  push up the curved surfaces  50   g  of the restricting projections  50   d  of the restricting members  50 . The restricting members  50 , which has been pushed up, are turned in the direction where they project outward against the biasing forces of the biasing members  51 . Such a state is shown by a two-dot chain line in FIG.  23 . When the lower edges of both the side surfaces of the sub-tray  18  reach the upper surfaces  50   f  of the restricting members  50 , the restricting members  50  are returned to the original positions by the biasing forces of the biasing members  51 , so that the sub-tray  18  is placed on the upper surfaces  50   f  of the restricting members  50 , with a result that the sub-tray  18  is contained in the second containing portion  41   b  (see FIG.  24 ). 
     When the sub-tray  18  is contained in the second containing portion  41   b , the unit holder  20  is no longer moved up. If the two sub-trays  18  are contained in the second and third containing portions  41   b  and  41   c  and no sub-tray  18  is contained in the first containing portion  41   a , when the sub-tray  18  contained in the third containing portion  41   c  is lifted up to the second containing portion  41   b , the sub-tray  18  contained in the second containing portion  41   b  is lifted up by the sub-tray  18  thus pushed up, to be contained in the first containing portion  41   a.    
     As described above, the restricting members  50  and the biasing members  51  are provided as holding/movement restricting means for holding the sub-tray  18  having been lifted up in the stocker  41  and restricting the movement of the sub-tray  18  in the downward direction opposed to the lift-up direction. The holding/movement restricting operation of the sub-tray  18  can be thus simply performed by combination of the above-described two kinds of members. This makes it possible to certainly hold the sub-tray  18  and restrict the movement of the sub-tray  18  with a simple configuration at a low production cost. 
     Two lifting/lowering sliders  52  are longitudinally slidably supported in the right and left slider arrangement groove portions  5   b  of the housing  2  (see FIGS.  28  and  29 ). 
     Each of the lifting/lowering sliders  52  has, in the inner surface, two cam grooves  53  and  54  for the unit holder which are spaced from each other in the longitudinal direction (see FIG.  28 ). The pins  21   a  and  21   b  to be supported, which are provided on each of the side surfaces of the unit holder  20 , are slidably fitted in the cam grooves  53  and  54  of the slider  52 , respectively. 
     The cam groove  53  for the unit holder has three cam groove portions continuous to each other: an upper side horizontal portion  53   a , a tilt portion  53   b  tilted forward, downward from the front end of the upper side horizontal portion  53   a , and a lower side horizontal portion  53   c  extending horizontally from the front end of the tilt portion  53   b . The cam groove  54  for the unit holder has five groove portions continuous to each other: an upper side horizontal portion  54   a , a tilt portion  54   b  tilted forward, downward from the front end of the upper side horizontal portion  54   a , a lower side horizontal portion  54   c  extending horizontally from the front end of the tilt portion  54   b , a lower side tilt portion  54   d  tilted forward, downward from the front end of the lower side horizontal portion  54   c , and a horizontal lowermost portion  54   e  extending horizontally from the front end of the lower side tilt portion  54   d . The upper side horizontal portion  53   a  and the upper side horizontal portion  54   a  are located at the same height, and the lower side horizontal portion  53   c  and the lower side horizontal portion  54   c  are located at the same height. 
     The inner surface of the lifting/lowering slider  52  has, on a rear half of a lower end portion, a rack portion  55  (see FIG.  28 ). 
     The outer surface of the lifting/lowering slider  52  has a cam groove  56  for a lock releasing lever to be described later, a cam groove  57  for the stocker, and a dual purpose cam groove  58 , which are arranged in this order from the front side (see FIG.  29 ). 
     The cam groove  56  for the lock releasing lever has three groove portions continuous to each other: an upper side horizontal portion  56   a , a tilt portion  56   b  tilted forward, downward from the front end of the upper side horizontal portion  56   a , and a lower side horizontal portion  56   c  extending horizontally from the front end of the tilt portion  56   b.    
     The cam groove  57  for the stocker has five groove portions continuous to each other: an upper side horizontal portion  57   a , an upper side tilt portion  57   b  tilted forward, downward from the front end of the upper side horizontal portion  57   a , an intermediate horizontal portion  57   c  extending horizontally from the front end of the upper side tilt portion  57   b , a lower side tilt portion  57   d  tilted forward, downward from the front end of the intermediate horizontal portion  57   c , and a lower side horizontal portion  57   e  extending horizontally from the front end of the lower side tilt portion  57   d.    
     The duel purpose groove  58  has five groove portions continuous to each other: an upper side horizontal portion  58   a , an upper side tilt portion  58   b  tilted forward, downward from the front end of the upper side horizontal portion  58   a , an intermediate horizontal portion  58   c  extending horizontally from the front end of the upper side tilt portion  58   b , a lower side tilt portion  58   d  tilted forward, downward from the front end of the intermediate horizontal portion  58   c , and a lower side horizontal portion  58   e  extending horizontally from the front end of the lower side tilt portion  58   d . The lower side horizontal portion  58   e  is longer in the longitudinal direction from the lower side horizontal portion  57   e  of the cam groove  57  for the stocker. 
     The pins  43   c  and  43   d  to be supported, which are provided on each of the right and left sides of the stocker  41 , are slidably engaged in the cam groove  57  for the stocker and the duel purpose cam groove  58 . The shaft portions  48   b  of the hold-down members  47  supported by each of the right and left sides of the stocker  41  are slidably engaged in the duel purpose groove  58 . 
     A lock releasing lever  59  is turnably supported by each of the lever supporting pins  4   b  of the housing  2  (see FIGS.  30  and  58 ). The lock releasing lever  59  extends longer in one direction, and an approximately central portion in the longitudinal direction is supported by the lever supporting pin  4   b . The lock releasing lever  59  has, at a front end portion, a shaft portion  59   a  to be supported which projects inward and has, at a rear end portion, a pressing portion  59   b . The shaft portion  59   a  to be supported of the lock releasing lever  59  is slidably engaged in the cam groove  56  for the lock releasing lever. 
     A switching circuit board  60  is mounted at a right end portion on the upper surface of the arrangement plate portion  5  of the housing  2  (see FIG.  31 ). A first switch  61  and a second switch  62  are provided on the switching circuit board  60  in such a manner as to be spaced from each other in the longitudinal direction (see FIGS.  31  and  32 ). 
     A switching gear  63  is supported on the upper surface of the arrangement plate portion  5  at a position located immediately on the left side of the switching circuit board  60  (see FIGS.  31  and  32 ). A first operating piece  63   a  and a second operating piece  63   b  are provided on the peripheral edge of the switching gear  63  in such a manner as to be spaced from each other in the circumferential direction. The length of the first operating piece  63   a  in the circumferential direction is longer than the length of the second operating piece  63   b  in the circumferential direction. 
     A pulley member  64  is supported on the upper surface of the arrangement plate portion  5 . The pulley member  64  integrally includes a pulley portion  64   a  positioned on the upper side and a gear portion  64   b  positioned on the lower side (see FIGS.  31  and  32 ). 
     A first intermediate gear  65 , which is configured as a two-stepped gear, is supported on the arrangement plate portion  5 , and an upper gear portion of the first intermediate gear  65  is meshed with the gear portion  64   b  of the pulley member  64  (see FIGS.  31  and  32 ). A second intermediate gear  66 , which is configured as a two-stepped gear, is supported on the arrangement plate portion  5 , and an upper gear portion  66   a  of the second intermediate gear  66  is meshed with the lower gear portion of the first intermediate gear  65  (see FIGS.  31  and  32 ). 
     The second intermediate gear  66  is arranged such that the upper gear portion  66   a  is positioned on the upper surface side of the arrangement plate portion  5 , and the lower gear portion  66   b  passes through the second gear insertion hole  5   f  to be positioned on the lower surface side of the arrangement plate portion  5 . 
     A drive motor  67  is mounted to a rear end portion on the back surface of the arrangement plate portion  5  (see FIG.  31 ). A motor shaft of the drive motor  67  passes through the motor shaft insertion hole  5   d , and a small pulley  68  is fixed to an upper end portion of the motor shaft. A belt  69  is wound between the small pulley  68  and the pulley portion  64   a  of the pulley member  64  (see FIG.  31 ). 
     A drive force transmission slider  70  is supported on the back surface of the arrangement plate portion  5  in such a manner as to be movable in the longitudinal direction (see FIGS. 33 to  35 ). The drive force transmission slider  70  integrally includes a vertically-elongated rectangular plate portion  71  to be supported and two projecting plate portions  72  projecting rightward and leftward from the front half of the rectangular plate portion  71  to be supported. An escape hole  71   a  extending longer in the longitudinal direction is formed in a central portion in the longitudinal direction of the rectangular plate portion  71  to be supported. An engagement projection  71   b  projecting upward is provided at the front side opening edge of the escape hole  71   a . The back surface of the rectangular plate portion  71  to be supported has, on the front and rear sides of the escape hole  71   a , two grooves  71   c  to be guided. Two rack portions  72   a  are formed on both the right and left edges of the projecting plate portions  72 . 
     Two transmission gears  73  are supported on a front end portion of the back surface of the arrangement plate portion  5  in such a manner as to be spaced from each other in the lateral direction (see FIG.  33 ). Each transmission gear  73  integrally includes a small gear  73   a  located on the upper side and a large gear  73   b  located on the lower side. The small gear  73   a  is meshed with the rack portion  72   a  on each of the right and left sides of the driver force transmission slider  70 . The large gear  73   b  of the transmission gear  73  is meshed with the rack portion  55  of each of the lifting/lowering sliders  52 . 
     A cam gear  74  is supported on the back surface of the arrangement plate portion  5  while covering, from below, the driver force transmission slider  70  (see FIGS. 33,  36  and  37 ). The cam gear  74  integrally includes a small gear portion  75  located on the upper side and a large gear portion  76  located on the lower side. The small gear portion  75 , which passes through the first gear insertion hole  5   e , is disposed on the upper surface side of the arrangement plate portion  5  and is meshed with the switching gear  63 . An engagement pin  77  is provided at a position offset radially from the center on the back surface of the large gear portion  76  (see FIG.  37 ). 
     The upper surface of the cam gear  74  has a cam groove  78  (see FIG.  36 ). The cam groove  78  has a circular-arc shaped non-operational portion  78  located at a position offset to the center side of the cam gear  74 ; a first unit lifting/lowering portion  78   b  continuous to the non-operational portion  78   a  and displaced to the center side; a second unit lifting/lowering portion  78   c  continuous to the first unit lifting/lowering portion  78   b  and displaced to the outer peripheral side; a first circular-arc portion  78   d  continuous to the second unit lifting/lowering portion  78   c  and located outside the non-operational portion  78   a ; a second circular-arc portion  78   e  located outside the first circular-arc portion  78   d ; and a third circular-arc portion  78   f  located outside the second circular-arc portion  78   e . The starting ends (that is, the ends on the unit lifting/lowering portion  78   c  and the ends on the opposed side) of the first circular-arc portion  78   d , second circular-arc portion  78   e , and third circular-arc portion  78   f  are continuous to each other. The length of the second unit lifting/lowering portion  78   c  is slightly longer than the length of the first unit lifting/lowering portion  78   b.    
     The engagement projection  71   b  of the driver force transmission slider  70  is slidably engaged in the cam groove  78  of the cam gear  74 . 
     A slider  79  for movement is supported on the guide rails  5   c  provided on the back surface of the housing  2  in such a manner as to be movable in the longitudinal direction (see FIGS.  38  and  39 ). The slider  79  for movement integrally includes a horizontally-elongated rectangular main plate portion  80  and two projections  81  to be guided which project forward from both the side edges of the main plate portion  80 . 
     The main plate portion  80  has, in a central portion in the lateral direction, a cam groove portion  82 . The cam groove portion  82  has a starting end portion  83  positioned on the front end side and extending in the lateral direction, a front side circular-arc portion  84  continuous to the left end of the starting end portion  83  and formed into a large semicircular-arc shape projecting leftward, a rear side circular-arc portion  85  continuous to the rear end of the front side circular-arc portion  84  and projecting obliquely rightward, forward, and a trailing end portion  86  continuous to the rear side circular-arc portion  85  and extending in the lateral direction. 
     A circular-arc first projection  83   a  projecting slightly rearward is provided at a left end portion of the front side inner surface of the starting end portion  83 . A left half  83   b  of the starting end portion  83  is wider than the other portion of the starting end portion  83 , and a rear side inner surface  83   c  is formed into an obtusely circular shape projecting rearward. A circular-arc shaped second projection  85   a  projecting slightly forward is provided at a left end portion of the rear inner surface of the rear side circular-arc portion  85 . 
     Each of the projections  81  to be guided of the slider  79  for movement has a groove  81   a  to be guided which is opened upward and extends in the longitudinal direction. The grooves  81   a  to be guided are slidably engaged on the guide rails  5   c  of the housing  2 . The projection  81  to be guided has, at a position near the front end, a connecting recess  81   b  opened outward. 
     The slider  79  for movement, which is movably supported by the housing  2 , is pressed, from below, by part of a slip-off preventive member (not shown) in order to be prevented from being slipped off from the housing  2 . 
     Two drive racks  87  are supported on the guide rails  4   d  provided on the side surface portions  4  of the housing  2  in such a manner as to be movable in the longitudinal direction (see FIGS. 40 to  42 ). Each of the drive racks  87  extends longer in the longitudinal direction. A rack portion  87   a  is formed on the upper edge of the drive rack  87  except for both end portions in the longitudinal direction. The drive rack  87  has, at a central portion in the longitudinal direction on the inner surface, a connecting pin  87   b  projecting inward. The drive rack  87  also has, in the inner surface, a groove  87   c  to be guided which extends in the longitudinal direction. 
     The groove  87   c  to be guided of the drive rack  87  is slidably supported on the guide rail  4   d . The connecting pin  87   b  of the drive rack  87  is connected in the connecting recess  81   b  of the slider  79  for movement. In the state that the drive rack  87  is supported on the guide rail  4   d  in such a state, the drive rack  87  is moved in the longitudinal direction along with the movement of the slider  70  for movement. The drive rack  87  is held down, from side, by part of the above-described slip-off preventive member, to be thus prevented from being slipped off from the housing  2 . 
     A first side surface gear  88  and a second side surface gear  89  are supported on each of the side surfaces  4  of the housing  2 . The first side surface gear  88  is a two-stepped gear having a small gear  88   a  and a large gear  88   b . The rack portion  87   a  of each drive rack  87  is meshed with the small gear  88   a  (see FIG.  42 ). The second side surface gear  89  is a two-stepped gear having a small gear  89   a  and a large gear  89   b . The large gear  88   b  of the first side surface gear  88  is meshed with the small gear  89   a , and the large gear  89   b  is meshed with the rack portion  17   d  of each of the rack members  17  supported by the main tray  8  (see FIG.  8 ). When the main tray  8  is moved in the longitudinal direction, the large gear  89   b  is released from the rack portion  17   d  of the rack member  17  and is meshed with the rack portion  14   a  of the main tray  8 . 
     When the drive motor  67  is rotated, the drive force of the drive motor  67  is transmitted to the second intermediate gear  66  via the small pulley  68 , the belt  69 , the pulley member  64 , and the first intermediate gear  65 , to rotate the cam gear  74  meshed with the lower side gear portion  66   b  of the second intermediate gear  66 . When the cam gear  74  is rotated, the switching gear  63  is rotated, to switch the first switch  61  and the second switch  62  from each other. 
     At the same time when the cam gear  74  is rotated, the drive force transmission slider  70  or the slider  79  for movement is selectively moved in the longitudinal direction. 
     When the drive force transmission slider  70  is moved, the transmission gears  73  meshed with the rack portions  72   a  of the drove force transmission slider  70  are rotated, to move the lifting/lowering sliders  52  in the longitudinal direction so as to lift/lower the unit holder  20 , turn the chucking member  31 , lift/lower the stocker  41 , or lift the sub-tray  18  contained in the stocker  41 . 
     On the other hand, when the slider  79  for movement is moved, the sub-tray  18  is moved in the longitudinal direction singly or integrally with the main tray  8  via the drive racks  87  connected to the slider  79  for movement, the first side surface gears  88 , and the second side surfaces  89 . 
     A control circuit board  90  is provided on the back surface of the base unit  24  (see FIG.  43 ). A relay board  91  is mounted on the back surface of a front end portion of the housing  2 , and the control circuit board  90  is connected to the relay board  91  via a flexible printed board  92  (see FIG. 43) Another flexible printed board (not shown) is led from the relay board  91 , and the relay board  91  is connected to a main board (not shown) for performing overall control of the acoustic equipment  100  via the flexible printed board. 
     A rear surface panel  93  is mounted on a rear end portion of the housing  2  (see FIG.  44 ). Sensors  94 ,  95  and  96  are provided on the front surface of the rear surface panel  93  in such a manner as to be spaced from each other in the lateral direction. The sensors  94 ,  95  and  96  are provided at positions corresponding to positions in the lateral direction of the light shielding projecting pieces  18   g ,  18   g  and  18   i  provided on the sub-trays  18 A,  18 B and  18 C. When each of the light shielding projecting pieces  18   g ,  18   h  and  18   i  of the sub-trays  18 A,  18 B and  18 C is vertically moved in a slit of the corresponding one of the sensors  94 ,  95  and  96 , detection light emitted from the sensor is shielded, whereby it can be decided which one of the sub-trays  18 A,  18 B and  18 C is moving. 
     The operation of the disc changer apparatus  1  will be hereinafter described. In the following description, for an easy understanding, it is assumed that a state that the main tray  8  is pulled out together with the sub-tray  18  and is located at a pull-out position is taken as an initial state. 
     In the state that the main tray  8  is pulled out of the housing  2 , that is, when the main tray  8  is located at a pull-out position together with the sub-tray  18 , since the shaft portions  59   a  to be supported of the lock releasing levers  59  are engaged with the front end portions of the upper side horizontal portions  56   a  of the cam grooves  56  (for the lever) of the lifting/lowering sliders  52  to be thus kept in an approximately horizontal state (see FIG.  47 ), the pressing portions  59   b  are spaced from the lock levers  15 . Accordingly, the lock projections  15   d  of the lock levers  15  biased by the torsion coil springs  16  are engaged in the locking recesses  18   e , whereby the sub-tray  18  is locked with the main tray  8 . Also, the connecting portions  17   c  of the rack members  17  are engaged in the connecting grooves  18   c  of the sub-tray  18 , and thereby the rack members  17  are positioned at the front ends of the movement ranges of the rack members  17  (see FIG.  45 ). At this time, the second surface gears  89  are meshed with the rear end portions of the rack portions  14   a  of the main tray  8  (see FIG.  45 ). 
     The unit holder  20  is located at a lower position, and in this state, the pins  21   a  and  21   b  to be supported, on each of side surfaces, of the unit holder  20  are engaged in the lower side horizontal portions  53   c  and  54   c  of the cam grooves  53  and  54  (for the unit holder) of each lifting/lowering slider  52 , respectively (see FIG.  46 ). The stocker  41  is located at the upper end of the movement range thereof, and in this state, the pins  43   c  and  43   d  to be supported, on each of the side surfaces, of the stocker  41  are respectively engaged in the approximately central portions in the longitudinal direction of the upper side horizontal portions  57   a  and  58   a  of the cam groove  57  for the stocker and the duel purpose groove  58  of each lifting/lowering slider  52  (see FIG.  47 ). 
     The hold-down members  47  supported by the stocker  41  are located at positions near the lower ends of the movement ranges thereof, and the shaft portions  48   b  are engaged in portions near the lower ends of the lower side tilt portions  58   d  of the duel purpose cam grooves  58  (see FIG.  47 ). Accordingly, the portions  34   a  to be held down of the chucking member  31  are held down, from above, by the hold-down pieces  48   a  of the hold-down members  47 , so that the chucking pulley  35  is located on the upper side of the movement range thereof (see FIGS.  46  and  47 ). In addition, when the hold-down members  47  are located on the upper side, since the movement restricting portions  49   a  of the hold-down members  47  are inserted in the connecting grooves  18   c  of the sub-tray  18  contained in the stocker  41 , the movement of the sub-tray  18  from the stocker  41  is restricted. 
     At this time, the slider  79  for movement is located at the front end of the movement range thereof, and the engagement pin  77  of the cam gear  74  is engaged in the trailing end portion  86  of the cam groove portion  82  of the slider  79  for the movement (see FIG.  48 ). The engagement projection  71   b  of the drive force transmission slider  70  is engaged in the starting end of the non-operational portion  78   a  of the cam gear  74 , and located at an intermediate portion of the movement range thereof (see FIG.  48 ). 
     The first switch  61  and the second switch  62  provided on the switching circuit board  60  are brought into contact with the second operating piece  63   b  and the first operating piece  63   a  of the switching gear  63  to be turned on, respectively. 
     In addition, when the main tray  8  is located at the pull-out position, if any disc-like recording medium is not mounted on the sub-tray  18 , a user can mount a disc-like recording medium on the sub-tray  18 , and if a disc-like recording medium has been already mounted on the sub-tray  18 , the user can mount another disc-like recording medium. Further, in the above-described state that the main tray  8  is located at the pull-out position, it is assumed that in the stocker  41 , the first and second containing portions  41   a  and  41   b  have already contained the sub-trays  18  and the third containing portion  41   c  is opened (see FIGS.  45  and  47 ). 
     When the drive motor  67  is rotated in one direction in the state that the main tray  8  is located at the pull-out position, the cam gear  74  is rotated in a direction R 1  shown in FIG. 48, so that the engagement pin  77  of the cam gear  74  is moved from the trailing end portion  86  to the rear side circular-arc portion  85  of the cam groove portion  82  of the slider  79  for movement while pressing the inner surfaces of these portions  86  and  85  of the cam groove portion  82 , with a result that the slider  79  for movement is moved rearward. Accordingly, the second surface side gears  89  meshed with the rack portions  14   a  of the main tray  8  are rotated to move the main tray  8  rearward together with the sub-tray  18 , whereby the main tray  8  and the sub-tray  18  are pulled in the housing  2  up to the disc mounting position (see FIG.  49 ). When the main tray  8  reaches the disc mounting position, the notch portion  14   a  is located at a position corresponding to that of each second side surface gear  89 , so that the second side surface gear  89  is meshed with the rack portion  17   d  of the rack member  17  supported by the main tray  8  (see FIG.  49 ). 
     The user can manually move the main tray  8  located at the pull-out position to the disc mounting position by pressing the main tray  8  rearward. At this time, the engagement pin  77  of the cam gear  74  is moved from the trailing end portion  86  to the rear side circular-arc portion  85  of the cam groove portion  82  of the slider  79  for movement while pressing these portions  86  and  85  of the cam groove portion  82 . In this case, since the rear side circular-arc portion  85  is formed into the obtusely circular-arc shape, the pressing load becomes small. As a result, it is possible to easily perform manual movement of the main tray  8  with a small force. 
     Even when the cam gear  74  is rotated as described above, the drive force transmission slider  70  is not moved in the longitudinal direction because the engagement projection  71   b  is relatively moved in the non-operational portion  78   a  of the cam groove  78 . Accordingly, the positions of the unit holder  20 , the chucking member  31 , and the stocker  41  are not changed. 
     When the slider  79  for movement is moved rearward, the engagement pin  77  of the cam gear  74  is slightly moved from the trailing end portion  86  to the rear side circular-arc portion  85  of the cam groove portion  82  of the slider  79  for movement, and when the main tray  8  reaches the disc mounting position, the engagement pin  77  is positioned in the rear side circular-arc portion  85  (see FIG.  50 ). Further, when the main tray  8  reaches the disc mounting position, the engagement projection  71   b  of the slider  70  for movement is positioned at an intersection between the non-operational portion  78   a  of the cam groove  78  and the first unit lifting/lowering portion  78   b  (see FIG.  50 ). 
     On the other hand, the switching gear  63  is rotated by rotation of the cam gear  74 , and when the main tray  8  reaches the disc mounting position, the second operating piece  63   b  of the switching gear  63   b  is separated from the first switch  61  to be turned off. At this time, the first operating piece  63   a  of the switching gear  63  is kept in contact with the second switch  62 , that is, left turned off. 
     When the drive motor  67  is further rotated in the one direction after the main tray  8  is moved to the disc mounting position, the cam gear  74  is rotated in an R 1  direction shown in FIG. 50, so that the engagement pin  77  of the cam gear  74  is relatively moved from the rear side circular-arc portion  85  to the front side circular-arc portion  84  of the cam groove portion  82  of the slider  79  for movement (see FIG.  55 ). Accordingly, the slider  79  for movement is no longer moved in the longitudinal direction, whereby the main tray  8  and the sub-tray  18  are held at the disc mounting position. 
     Along with the rotation of the cam gear  74 , the engagement projection  71   b  of the drive force transmission slider  70  is relatively moved in the first unit lifting/lowering portion  78   b  of the cam groove  78 , and thereby the drive force transmission slider  70  is moved rearward and the lifting/lowering sliders  52  are moved forward. Along with the forward movement of the lifting/lowering sliders  52 , the shaft portions  48   b  of the hold-down members  47  supported on each of the right and left sides of the stocker  41  are moved from the lower side tilt portion  58   d  to the intermediate horizontal portion  58   c  of the duel purpose cam groove  58   d  (see FIG.  51 ), and further relatively moved from the upper side tilt portion  58   b  to the upper side horizontal portion  58   a  of the duel purpose cam groove  58  (see FIG.  52 ). Accordingly, the hold-down members  47  are moved up, and the chucking member  31  is turned in the direction where the front end portion of the chucking member  31  is moved down (see FIGS.  52  and  53 ). 
     On the other hand, even when the lifting/lowering sliders  52  are moved forward, the pins  43   c  and  43   d  to be supported, on each of the side surfaces, of the stocker  41  are relatively moved in the upper side horizontal portions  57   a  and  58   a  of the cam groove  57  for the stocker and the duel purpose cam groove  58  of each lifting/lowering slider  52 , respectively, and accordingly, the pins  43   c  and  43   d  to be supported of the stocker  41  are not moved in the vertical direction and held at the movement ends thereof on the upper sides. 
     Along with the forward movement of the lifting/lowering sliders  52 , the pins  21   a  and  21   b  to be supported, on each of the side surfaces, of the unit holder  20  are relatively moved from the lower side horizontal portions  53   c  and  54   c  to the upper side horizontal portions  53   a  and  54   a  via the tilt portions  53   b  and  54   b  of the cam grooves  53  and  54  for the unit holder, respectively (see FIG.  53 ). Accordingly, the unit holder  20  is lifted, and the disc table  28  is inserted in the center hole of the disc-like recording medium mounted on the sub-tray  18 . Further, along with the lifting of the unit folder, the disc-like recording medium is separated upward from the sub-tray  18  and is held, that is, chucked between the disc table  28  and the chucking pulley  35  (see FIG.  53 ). At this time, the iron plate  40  provided on the chucking pulley  35  is attracted by the magnet  28   a  provided on the disc table  28  and also the disc-like recording medium is held on the magnet  28   a  in a state that the rubber  39  is in contact with the upper surface of the disc-like recording medium. 
     When the unit holder  20  is lifted, the positioning projections  21   d  provided on the unit holder  20  are inserted, from below, in the positioning holes  9   c  and the positioning holes  12   a  (vertically overlapped to the positioning holes  9   c ) of the main tray  8  and the positioning holes  18   d  of the sub-tray  18 . Further, the positioning projections  21   e  of the unit holder  20  is brought into sliding-contact with the rear edge of the sub-tray  18 , whereby the unit holder  20  is positioned to the sub-tray  18  (see FIG.  54 ). In this case, as described above, since the upper surfaces of the positioning projections  21   d  and  21   e  are tilted, the positioning projections  21   d  of the unit holder  20  can be certainly inserted in the positioning holes  9   c  and  12   a  of the main tray  8  and the positioning holes  18   d  of the sub-tray  18 , and the positioning projections  21   e  of the unit holder  20  can be certainly brought into contact with the rear edge of the sub-tray  18 . 
     Accordingly, the disc table  28  can be certainly inserted in the center hole of the disc-like recording medium mounted on the sub-tray  18 , and the disc-like recording medium can be certainly chucked. 
     In addition, when the unit holder  20  is lifted, the positioning projections  21   f  provided at the rear end portion of the unit holder  20  are inserted, from below, in the positioning holes  18   d  of the sub-trays  18  contained in the stocker  41 , whereby the movement of the sub-trays  18  in the longitudinal direction is restricted (see FIG.  54 ). 
     Along with the rotation of the cam gear  74 , the engagement projection  71   b  of the drive force transmission slider  70  is relatively moved in the first unit lifting/lowering portion  78   b  of the cam groove  78 , and when the disc-like recording medium is chucked, the engagement projection  71   b  is positioned at an intersection between the first unit lifting/lowering portion  78   b  and the second unit lifting/lowering portion  78   c , that is, at a position, closest to the center portion of the cam gear  74 , of the cam groove  74  (see FIG. 55) Accordingly, the lifting/lowering sliders  52  are no longer moved forward and are positioned at the front ends of the movement ranges thereof. 
     After the disc-like recording medium is chucked by the disc table  28  and the chucking pulley  35  as described above, the disc-like recording medium thus chucked is rotated by the spindle motor  27  and simultaneously information signals recorded on the disc-like recording medium are reproduced by drive of the optical pickup. 
     On the other hand, when the switching gear  63  is rotated by rotation of the cam gear  74  and the disc-like recording medium is chucked, the first and second operating pieces  63   a  and  63   b  do not operate, that is, turn off the first and second switches  61  and  62 , respectively (see FIG.  55 ). As a result, it is detected that the disc-like recording medium is located at the reproducing position. 
     When the drive motor  67  is further rotated in the one direction after the reproducing of the information signals recorded on the disc-like recording medium is ended, the cam gear  74  is rotated in the R 1  direction shown in FIG. 55, so that the engagement pin  77  of the cam gear  74  is further relatively moved in the front side circular-arc portion  84  of the cam groove portion  82  of the slider  79  for movement. Accordingly, the slider  79  for movement is not moved in the longitudinal direction and thereby the main tray  8  and the sub-tray  18  are held at the mounted positions. 
     Along with the rotation of the cam gear  74 , the engagement projection  71   b  of the drive force transmission slider  70  is relatively moved in the unit lifting/lowering portion  78   c  of the cam groove  78 , so that the drive force transmission slider  70  is moved forward and the lifting/lowering sliders  52  are moved rearward. When the lifting/lowering sliders  52  are moved rearward, the shaft portions  48   b  of the hold-down members  47  supported on each of the right and left sides of the stocker  41  are moved from the upper side horizontal portion  58   a  to the lower side horizontal portion  58   e  of the duel purpose cam groove  58  (see FIG. 56) of each lifting/lowering slider  52 . Accordingly, the hold-down members  47  are moved down and thereby the chucking member  31  is turned in the direction being separated from the disc table  28 . The chucking of the disc-like recording medium is thus released. 
     On the other hand, even when the lifting/lowering sliders  52  are moved rearward, the pins  43   c  and  43   d  to be supported, on each of the side surfaces, of the stocker  41  are relatively moved in the upper side horizontal portions  57   a  and  58   a  of the cam groove  57  for the stocker and the duel purpose cam groove  58  of each lifting/lowering slider  52 , respectively, and accordingly, the pins  43   c  and  43   d  to be supported of the stocker  41  are not moved in the vertical direction and held at the movement ends on the upper sides. 
     Along with the rearward movement of the lifting/lowering sliders  52 , the pins  21   a  and  21   b  to be supported, on each of the side surfaces, of the unit holder  20  are relatively moved from the upper side horizontal portions  53   c  and  54   c  to the lower side horizontal portions  53   a  and  54   a  via the tilt portions  53   b  and  54   b  of the cam grooves  53  and  54  (for the unit holder) of each lifting/lowering slider  52 , respectively. Accordingly, the unit holder  20  is lowered, and thereby the disc-like recording medium is mounted again in the sub-tray  18  and the disc table  28  is moved down from the sub-tray  18 . 
     When the unit holder  20  is lowered, the positioning projections  21   d ,  21   e , and  21   f  provided on the unit holder  20  are also lowered. 
     Along with the rotation of the cam gear  74 , the engagement projection  71   b  of the drive force transmission slider  70  is relatively moved in the second unit lifting/lowering portion  78   c  of the cam groove  78 , and when the unit holder  20  is lowered, the engagement projection  71   b  is relatively moved to a position near the intersection between the second unit lifting/lowering portion  78   c  and the first circular-arc portion  78   d  (see FIG.  57 ). 
     On the other hand, along with the rotation of the cam gear  74 , the switching gear  63  is rotated, and when the unit holder  20  is lowered and the chucking of the disc-like recording medium is released, the first operating piece  63   a  is brought into contact with the first switch  61  to turn on the first switch  61 , with the second switch  62  left turned off (see FIG.  57 ). 
     Since the length of the second unit lifting/lowering portion  78   c  is slightly longer than the length of the first unit lifting/lowering portion  78   b  as described above, when the unit holder  20  is lowered, each lifting/lowering slider  52  is moved rearward over the position thereof on the initial state. Accordingly, the lock releasing lever  59  is relatively moved from the upper side horizontal portion  56   a  to the lower side horizontal portion  56   c  via the tilt portion  56   b  of the cam groove  56  (for the lever) of each lifting/lowering slider  52  (see FIG.  58 ). 
     When the shaft portion  59   a  to be supported of each lock releasing lever  59  is engaged in the lower side horizontal portion  56   c , the lock releasing lever  59  is turned in the direction where the pressing portion  59   b  is moved up, whereby the pressing portion  59   b  presses, from below, the portion  15   c  to be operated of the lock lever  15 . When the portions  15   c  to be operated of the lock levers  15  are pressed, the lock levers  15  are turned against the biasing forces of the torsion coil springs applied around the supporting shafts  15   a , to release the locking of the sub-tray  18  by the locking projections of the lock levers  15 . Further, since the pressing portions  59   b  of the lock releasing levers  59  come in proximity to or in contact with the front ends of the projecting pieces  9   f  to be restricted of the main tray  8 , the movement of the main tray  8  in the longitudinal direction is restricted (see FIG.  58 ). Accordingly, the sub-tray  18  and the main tray  8  are independently movable rearward. 
     When the drive motor  67  is further rotated in the one direction after the unit holder  20  is lowered as described above, the cam gear  74  is rotated in the R 1  direction shown in FIG. 57, so that the engagement pin  77  of the cam gear  74  is relatively moved from the front side circular-arc portion  84  to the starting end portion  83  of the cam groove portion  82  of the slider  79  for movement (see FIG.  61 ), to press the inner surface of the starting end portion  83  rearward, whereby the slider  79  for movement is moved rearward. Accordingly, the second side surface gears  89  meshed with the rack portions  17   d  of the rack members  17  are rotated, whereby the sub-tray  18  is singly moved rearward (see FIG.  59 ). At this time, since the third containing portion  41   c  of the stocker  41  is positioned at the back of the sub-tray  18 , the sub-tray  18  moved rearward is contained in the third containing portion  41   c  (see FIG.  60 ). 
     Even when the cam gear  74  is rotated as described above, since the engagement projection  71   b  of the drive force transmission slider  70  is relatively moved in the first circular-arc portion  78   d  of the cam groove  78 , the drive force transmission slider  70  is not moved in the longitudinal direction. Accordingly, the positions of the unit holder  20 , the chucking member  31  and the stocker  41  are not changed. 
     When the sub-tray  18  is contained in the stocker  41  and moved to a disc containing position and the slider  79  for movement is moved rearward to the movement end on the rear side, the engagement pin  77  of the cam gear  74  is positioned at an approximately central portion of the starting end portion  83  of the cam groove portion  82  of the slider  79  for movement (see FIG.  61 ). When the sub-tray  18  reaches the disc containing position, the engagement projection  71   b  of the drive force transmission slider  70  is positioned at the trailing end of the first circular-arc portion  78   d  of the cam groove  78  (see FIG.  61 ). 
     On the other hand, when the switching gear  63  is rotated by rotation of the cam gear  74  and the sub-tray  18  reaches the disc containing position, the first operating piece  63   a  is brought into contact with the first switch  61  to turn on the first switch  61  (see FIG.  61 ), with the second switch  62  lest turned off. 
     When the drive motor  67  is further rotated in the one direction after the sub-tray  18  is contained in the stocker  41 , the cam gear  74  is rotated in the R 1  direction shown in FIG. 61, so that the engagement pin  77  of the cam gear  74  is moved in the left half  83   b  of the starting end portion  83  of the cam groove portion  82  of the slider  79  for movement. As described above, the left half  83   b  of the starting end portion  83  is wider than the other portion of the starting end portion  83 , and the inner surface  83   c  is formed into a circular shape. As a result, when the cam gear  74  is rotated in the state that the sub-tray  18  is contained in the stocker  41 , the engagement pin  77  is moved while being not brought into contact with both the inner surfaces of the left half  83   b  (see FIG.  62 ), and accordingly the slider  79  for movement is stopped at the rear side movement end, with a result that the sub-tray  18  is not moved in the longitudinal direction. 
     When the cam gear  74  is rotated as described above, the engagement projection  71   b  of the drive force transmission slider  70  is relatively moved from the trailing end of the first circular-arc portion  78   d  to the second circular-arc portion  78   e  of the cam groove  78  (see FIG.  62 ), so that the drive force transmission slider  70  is moved forward and the lifting/lowering sliders  52  are moved rearward. When the lifting/lowering sliders  52  are moved rearward, the shaft portions  48   b  of the hold-down members  47  supported on each of the right and left sides of the stocker  41  are relatively moved forward in the lower side horizontal portion  58   e  of the duel purpose cam groove  58  of each lifting/lowering slider  52  (see FIG.  63 ). As a result, the hold-down members  47  are not moved in the vertical direction and thereby the chucking member  31  is held at the movement end on the upper side. 
     On the other hand, when the lifting/lowering sliders  52  are moved rearward, the pins  43   c  and  43   d  to be supported, on each of the side surfaces, of the stocker  41  are relatively moved from the upper side horizontal portions  57   a  and  58   a  to the intermediate horizontal portions  57   c  and  58   c  via the upper side tilt portions  57   b  and  58   b  of the cam groove  57  for the stocker and the duel purpose cam groove  58  of each lifting/lowering slider  52  (see FIG.  63 ). Accordingly, the stocker  41  is lowered to an intermediate height, so that the sub-tray  18  contained in the second containing portion  41   b  is positioned on the rear side of the main tray  8 . When the sub-tray  18  contained in the second containing portion  41   b  is positioned on the rear side of the main tray  8 , the connection of the connecting portions  17   c  of the rack members  17  of the main tray  8  into the connecting grooves  18   c  of the sub-tray  18  contained in the third containing portion  41   c  is released, and the connecting portions  17   c  of the rack members  17  of the main tray  8  are connected into the connecting grooves  18   c  of the sub-tray  18  contained in the second containing portion  41   b.    
     Along with the rearward movement of the lifting/lowering sliders  52 , the pins  21   a  and  21   b  to be supported, on each of the side surfaces, of the unit holder  20  are relatively moved in the lower side horizontal portions  53   c  and  54   c  of the cam grooves  53  and  54  (for the unit holder) of each of the lifting/lowering slider  52 , respectively. Accordingly, the unit holder  20  is not moved in the vertical direction. 
     On the other hand, when the switching gear  63  is rotated by rotation of the cam gear  74  and thereby the pins  43   c  and  43   d  to be supported, on each of the side surfaces, of the stocker  41  are relatively moved in the intermediate horizontal portions  57   c  and  58   c  of the cam groove  57  for the stocker and the duel purpose cam groove  58  of each lifting/lowering slider  52 , respectively, the first operating piece  63   a  is brought into contact with the first switch  61  to turn on the first switch  61  (see FIG.  62 ), with the second switch  62  left turned off. 
     At this time, the rotation of the drive motor  67  is once stopped, and when the drive motor  67  is rotated in the direction reversed to the above-described one direction, the sub-tray  18  contained in the second containing portion  41   b  of the stocker  41  is pulled out of the stocker  41  and is moved to the disc mounting position (see FIG.  64 ). 
     To be more specific, when the drive motor  67  is rotated in the direction reversed to the above-described one direction, the cam gear  74  is rotated in an R 2  direction shown in FIG. 62, so that the engagement pin  77  of the cam gear  74  presses forward the inner surface of the starting end portion  83  of the cam groove portion  82  of the slider  79  for movement. Accordingly, the slider  79  for movement is moved forward and thereby the second side surface gears  89  are rotated in the direction reversed to the above-described direction. As a result, the rack portions  17   d  of the rack members  17  are fed forward, whereby the sub-tray  18  is moved forward to the disc mounting position (see FIG.  64 ). When the sub-tray  18  reaches the disc mounting position, the sub-tray  18  is locked with the main tray  8  with the lock levers  15 . 
     When the sub-tray  18  reaches the disc mounting position, the engagement projection  71   b  of the drive force transmission slider  70  is positioned at the starting end of the second circular-arc portion  78   e  of the cam groove  78  (see FIG.  65 ). 
     When the sub-tray  18  contained in the second containing portion  41   b  is positioned on the rear side of the main tray  8  located in the state shown in FIG. 62, the drive motor  67  is not stopped and continuously rotated in the one direction. At this time, the cam gear  74  is rotated in the R 1  direction, so that like the above-described operation, the engagement pin  77  is moved while being not brought into contact with any of both the inner surfaces of the left half  83   b  (see FIG.  66 ). As a result, the slider  79  for movement is stopped at the movement end on the rear side, and thereby the sub-tray  18  is not moved in the longitudinal direction. 
     When the cam gear  74  is further rotated, the engagement projection  71   b  of the drive force transmission slider  70  is relatively moved to the trailing end of the third circular-arc portion  78   f  via the trailing end of the second circular-arc portion  78   e  of the cam groove  78  (see FIG.  66 ), so that the drive force transmission slider  70  is further moved forward and the lifting/lowering sliders  52  are further moved rearward. When the lifting/lowering sliders  52  are further moved rearward, the shaft portions  48   b  of the hold-down members  47  supported on each of the right and left sides of the stocker  41  are relatively moved in the lower side tilt portion  58   d  of the duel purpose cam groove  58  to reach the front end of the duel purpose groove  58  of each lifting/lowering slider  52  (see FIG.  67 ). Accordingly, the hold-down members  47  are not moved in the vertical direction and thereby the chucking member  31  is held at the movement end on the upper side. 
     On the other hand, when the lifting/lowering sliders  52  are further moved rearward, the pins  43   c  and  43   d  to be supported, on each of the side surfaces, of the stocker  41  are relatively moved to the lower side horizontal portions  57   e  and  58   e  via the intermediate horizontal portions  57   c  and  58   c  and the lower side tilt portions  57   d  and  58   d  of the cam groove  57  for the stocker and the duel purpose cam groove  58  of each lifting/lowering slider  52  (see FIG.  67 ). Accordingly, the stocker  41  is located at a further lower position, and the sub-tray  18  contained in the first containing portion  41   a  is position on the rear side of the main tray  8 . When the sub-tray  18  contained in the first containing portion  41   a  is positioned on the rear side of the main tray  8 , the connecting portions  17   c  of the rack members  17  are connected to the connecting grooves  18   c  of the sub-tray  18  contained in the first containing portion  41   a.    
     Along with the rearward movement of the lifting/lowering sliders  52 , the pin  21   a  to be supported, on each of the side surfaces of the unit holder  20 , is relatively moved forward in the lower side horizontal portion  53   c  of the cam groove  53  (for the unit holder) of each lifting/lowering slider  52 , and the pin  21   b  to be supported, on each of the side surfaces of the unit holder  20 , is moved from the lower side horizontal portion  54   c  to the lowermost portion  5   e  via the lower side tilt portion  54   d  of the cam groove  54  (for the unit holder) of each lifting/lowering slider  52 . Accordingly, the unit holder  20  is tilted rearward, downward (see FIG.  68 ). 
     Since the unit holder  20  is tilted rearward, downward as described above, the stocker  41  moving down is not brought into contact with the unit holder  20 . As a result, it is possible to realize the suitable downward movement of the stocker  41 . 
     On the other hand, the switching gear  63  is rotated by rotation of the cam gear  74 , and when the pins  43   c  and  43   d , on each of the right and left sides of the stocker  41 , are relatively moved in the lower side horizontal portions  57   e  and  58   e  of the cam groove  57  for the stocker and the duel purpose cam groove  58  of each lifting/lowering slider  52 , respectively, the first operating piece  63   a  is brought into contact with the first switch  61  to turn on the first switch  61 , with the second switch  62  left turned off. 
     At this time, the rotation of the drive motor  67  is once stopped, and when the drive motor  67  is rotated in the direction reversed to the one direction, the sub-tray  18  contained in the first containing portion  41   a  of the stocker  41  is pulled out of the stocker  41  and is moved to the disc mounting position (see FIG.  69 ). 
     To be more specific, when the drive motor  67  is rotated in the direction reversed to the one direction, the cam gear  74  is rotated in the R 2  direction shown in FIG. 66, so that the engagement pin  77  of the cam gear  74  presses forward the inner surface of the starting end portion  83  of the cam groove portion  82  of the slider  79  for movement. Accordingly, the slider  79  for movement is moved forward, and thereby the rack members  17  are fed forward, with a result that the sub-tray  18  is moved forward to the disc mounting position (see FIG.  69 ). When the sub-tray  18  reaches the disc mounting position, the sub-tray  18  is locked with the main tray  8  by the lock levers  15 . 
     When the sub-tray  18  reaches the disc mounting position, the engagement projections  71   b  of the drive force transmission slider  70  is positioned at the starting end of the third circular-arc portion  78   f  of the cam groove  78  (see FIG.  70 ). 
     When the sub-tray  18  is moved rearward from the disc mounting position and contained in the third containing portion  41   c  of the stocker  41 , the drive motor  67  is once stopped and is then rotated in the direction reversed to the one direction. At this time, like the above-described operation, the engagement pin  77  presses forward the inner surface of the starting end portion  83  of the cam groove portion  82  of the slider  79  for movement, so that the slider  79  for movement is moved forward and thereby the sub-tray  18  contained in the third containing portion  41   c  is moved again to the disc mounting position. When the sub-tray  18  reaches the disc mounting position, the engagement pin  71   b  of the drive force transmission slider  70  is positioned at the starting end of the first circular-arc portion  78   d  of the cam groove  78 . 
     Even if either of the sub-trays  18  contained in the first, second, and third containing portions  41   a ,  41   b  and  41   c  of the stocker  41  is moved to the disc mounting position, when the drive motor  67  is further moved in the direction reversed to the one direction, the cam gear  74  is rotated in the R 2  direction, so that the engagement pin  77  of the cam gear  74  is relatively moved in the front side circular-arc portion  84  of the cam groove portion  82  of the slider  79  for the movement. Accordingly, the slider  79  for movement is not moved in the longitudinal direction and thereby the main tray  8  and the sub-tray  18  are held at the disc mounting positions. 
     On the other hand, when the drive motor  67  is further rotated in the direction reversed to the one direction, the cam gear  74  is rotated, so that the engagement projection  71   b  of the drive force transmission slider  70  is relatively moved in the second unit lifting/lowering portion  78   c  of the cam groove  78  toward the first unit lifting/lowering portion  78   b , with a result that the drive force transmission slider  70  is moved rearward and the lifting/lowering sliders  52  are moved forward. When the lifting/lowering sliders  52  are moved forward, the shaft portions  48   b  of the hold-down members  47  supported by each of the right and left sides of the stocker  41  are moved in the lower side horizontal portion  58   e  of the duel purpose cam groove  58  of each lifting/lowering slider  52 . Accordingly, the chucking member  31  is held on the upper side. 
     On the other hand, when the lifting/lowering sliders  52  are moved forward, the pins  43   c  and  43   d  to be supported, on each of the side surfaces, of the stocker  41  are relatively moved from the lower side horizontal portions  57   e  and  58   e  to the upper side horizontal portions  57   a  and  58   a  of the cam groove  57  for the stocker and the duel purpose cam groove  58  of each lifting/lowering slider  52 . Accordingly, the stocker  41  is moved to the upper end of the movement range thereof, and the third containing portion  41   c  is positioned on the rear side of the main tray  8 . At this time, the pin  21   a  to be supported, on each of the side surfaces of the unit holder  20 , is relatively moved in the lower side horizontal portion  53   c  of the cam groove  53  (for the unit holder) of each lifting/lowering slider  52 , while the pin  21   b  to be supported, on each of the side surfaces of the unit holder  20 , is moved from the lowermost portion  54   e  to the lower side horizontal portion  54   c  of the cam groove  54  (for the unit holder) of each lifting/lowering slider  52 . Accordingly, the unit holder  20 , which has been tilted rearward, downward, is held in the horizontal state. 
     The lifting/lowering sliders  52  are further moved forward, and the pins  21   a  and  21   b  to be supported, on each of the side surfaces, of the unit holder  20  are relatively moved from the lower side horizontal portions  53   c  and  54   c  to the upper side horizontal portions  53   a  and  54   a  via the tilt portions  53   b  and  54   b  of the cam grooves  53  and  54  (for the unit holder) of each lifting/lowering slider  52 , with a result that the unit holder  20  is lifted (see FIG.  71 ). The shaft portions  48   b  of the hold-down members  47  supported by each of the right and left sides of the stocker  41  are moved from the lower side horizontal portion  58   e  to the upper side horizontal portion  58   a  of the duel purpose cam groove  58  of each lifting/lowering slider  52 , and thereby the chucking member  31  is turned in the direction where the front end portion thereof is moved down. 
     Accordingly, when the disc-like recording medium is in the state being mounted on the sub-tray  18  having been moved to the disc mounting position, the disc-like recording medium is chucked by the disc table  28  and the chucking pulley  35  (see FIG.  71 ). 
     When the unit holder  20  is lifted, as described above, the sub-tray  18  is held in the third containing portion  41   c , and simultaneously, if the sub-tray  18  is not held in either the first containing portion  41   a  or the second containing portion  41   b , the sub-tray  18  is lifted up by the lift-up portions  23  of the unit holder  20 , whereby the third containing portion  41   c  is opened (see FIGS. 23,  24  and  71 ). Accordingly, when the sub-tray  18  is contained from the disc mounting position into the stocker  41 , the sub-tray  18  is usually contained in the third containing portion  41   c.    
     Along with the rotation of the cam gear  74 , the engagement projection  71   b  of the drive force transmission slider  70  is relatively moved in the second unit lifting/lowering portion  78   c  of the cam groove  78 , and when the unit holder  20  reaches the upper end, the engagement projection  71   b  is positioned at the intersection between the first unit lifting/lowering portion  78   b  and the second unit lifting/lowering portion  78   c  (see FIG.  55 ). Accordingly, the lifting/lowering sliders  52  are no longer moved forward, and located at the front ends of the movement ranges thereof. 
     When the disc-like recording medium is chucked between the disc table  28  and the chucking pulley  35  as described above, the disc-like recording medium thus chucked is rotated by rotation of the spindle motor  27 , and information signals recorded on the disc-like recording medium are reproduced by drive of the optical pickup  26 . 
     On the other hand, when the switching gear  63  is rotated by rotation of the cam gear  74  and the disc-like recording medium is chucked, the first and second operating pieces  63   a  and  63   b  do not operate the first and second switches  61  and  62  so that the first and second switches  61  and  62  are left turned off (see FIG.  55 ), which detects that the disc-like recording medium is located at the reproducing position. 
     When the unit holder  20  reaches the upper end and the drive motor  67  is rotated in the direction reversed to the one direction, the cam gear  74  is rotated, so that the engagement pin  77  of the cam gear  74  is relatively moved in the front side circular-arc portion  84  of the cam groove portion  82  of the slider  79  for movement. As a result, the slider  79  for movement is not moved in the longitudinal direction and thereby the main tray  8  and the sub-tray  18  are held at the disc mounting position. 
     Along with the rotation of the cam gear  74 , the engagement projection  71   b  of the drive force transmission slider  70  is relatively moved in the first unit lifting/lowering portion  78   b  toward the non-operational portion  78   a  of the cam groove  78 , and thereby the drive force transmission slider  70  is moved forward and the lifting/lowering sliders  52  are moved rearward. When the lifting/lowering sliders  52  are moved rearward, the shaft portions  48   b  of the hold-down members  47  supported by each of the right and left sides of the stocker  41  are moved from the upper side horizontal portion  58   a  to the lower side horizontal portion  58   e  of the duel purpose cam groove  58  of each lifting/lowering slider  52  (see FIG.  56 ). Accordingly, the hold-down members  47  are moved down and thereby the chucking member  31  is turned in the direction where the chucking member  31  is separated from the disc table  28 , to thereby release the chucking of the disc-like recording medium. 
     On the other hand, even when the lifting/lowering sliders  52  are moved rearward, since the pins  43   c  and  43   d  to be supported, on each of the side surfaces, of the stocker  41 , are relatively moved in the upper side horizontal portions  57   a  and  58   a  of the cam groove  57  for the stocker and the duel purpose cam groove  58  of each lifting/lowering slider  52 , respectively, the lifting/lowering sliders  52  are not moved in the vertical direction but are held at the upper movement ends. 
     Along with the rearward movement of the lifting/lowering sliders  52 , the pins  21   a  and  21   b  to be supported, on each of the side surfaces, of the stocker  41  are relatively moved from the upper side horizontal portions  53   c  and  54   c  to the lower side horizontal portions  53   a  and  54   a  via the tilt portions  53   b  and  54   b  of the cam grooves  53  and  54  (for the unit holder) of each lifting/lowering slider  52 . Accordingly, the unit holder  20  is lowered. 
     Along with the rotation of the cam gear  74 , the engagement projection  71   b  of the drive force transmission slider  70  is relatively moved in the first unit lifting/lowering portion  78   c  of the cam groove  78 , and when the unit holder  20  is lowered, the engagement projection  71   b  is relatively moved to the intersection between the first unit lifting/lowering portion  78   c  and the non-operational portion  78   a  (see FIG.  50 ). 
     On the other hand, the switching gear  63  is rotated by rotation of the cam gear  74 , and when the unit holder  20  is lowered, the first switch  61  is turned off and the second switch  62  is brought into contact with the first operating piece  63   a  to be turned on (see FIG.  50 ). 
     When the drive motor  67  is further rotated in the direction reversed to the one direction in the state that the main tray  8  and the sub-tray  18  are located at the disc mounting position, the cam gear  74  is rotated, so that the engagement pin  77  of the cam gear  74  is moved from the rear side circular-arc portion  85  to the trailing end portion  86  of the cam groove portion  82  of the slider  79  for movement while pressing the inner surfaces of the portions  85  and  86  forward, with a result that the slider  79  for movement is moved forward. At this time, the second side surface gears  89  are meshed with the rear end portions of the rack portions  17   d  of the rack members  17 , so that the second side surface gears  89  are rotated and thereby the rack members  17  are fed forward. Subsequently, the second side surface gears  89  are meshed with the rack portions  14   a  of the main tray  8 , whereby the main tray  8  is moved, together with the sub-tray  18 , to the pull-out position (see FIG.  45 ). 
     Even when the cam gear  74  is rotated as described above, since the engagement projection  71   b  of the drive force transmission slider  70  is relatively moved in the non-operational portion  78   a  of the cam groove  78 , the drive force transmission slider  70  is not moved in the longitudinal direction. Accordingly, the positions of the unit holder  20 , the chucking member  31 , and the stocker  41  are not changed. 
     When the slider  79  for movement is moved forward, the engagement pin  77  of the cam gear  74  presses the inner surface of the trailing end portion  86  of the cam groove portion  82  of the slider  79  for movement, and accordingly, when the main tray  8  reaches the pull-out position, the engagement pin  77  is positioned in the trailing end portion  86  (see FIG.  48 ). Further, when the main tray  8  reaches the pull-out position, the engagement projection  71   b  of the drive force transmission slider  70  is positioned at the starting end of the non-operational portion  78   a  of the cam groove  78  (see FIG.  48 ). 
     On the other hand, when the switching gear  63  is rotated by rotation of the cam gear  74  and the main tray  8  reaches the pull-out position, the first and second operating pieces  63   a  and  63   b  are brought into contact with the second and first switches  62  and  61  to turn on the second and first switches  62  and  61 , respectively. 
     As described above, according to the disc changer apparatus  1 , the sub-tray  18  having been moved rearward from the disc mounting position is usually contained in the third containing portion  41   c  of the stocker  41 . 
     Accordingly, unlike the related art disc changer apparatus in which a stocker is lifted/lowered to contain a tray in an empty containing portion, it is possible to eliminate the need of provision of a specialized lifting/lowering mechanism, a sensor for detecting an empty containing portion, and the like, and hence to correspondingly reduce the number of parts. This is advantageous in reducing the production cost. 
     Since the three sub-trays  18  can be stacked in the stocker  41  without use of roulette type trays serving as a stocker in consideration of reduction in the number of parts, the disc changer apparatus  1  can be miniaturized. 
     According to the disc changer apparatus  1 , the movement of the main tray  8  and the sub-tray  18 , the lifting/lowering of the unit holder  20 , the turning of the chucking member  31 , the lifting/lowering of the stocker  41 , and the upward movement of the two sub-trays  18  contained in the stocker  41  are made by using one drive motor  67 , it is possible to further reduce the number of parts. 
     As described above, when the sub-tray  18  is moved from the disc containing position to the disc mounting position, the slider  79  for movement is moved from the rear side to an approximately central portion in the longitudinal direction (hereinafter, referred to as “neutral area”). On the contrary, when the main tray  8  is moved from the main tray pull-out position to the disc mounting position, the slider  79  for movement is moved from the front side to the neutral area. 
     The above-described neutral area will be more fully described below. When the sub-tray  18  or the main tray  8  is moved, the second side surface gears  89  meshed with the rack portions  17   d  of the rack members  17  supported by the main tray  8  or the rack portions  14   a  of the main tray  8  are rotated, and in this case, as shown in FIGS. 72 and 73, a backlash “d” occurs between each gear tooth and the corresponding rack tooth. As a result, a slight deviation occurs between a longitudinal central position where the slider  79  for movement, which has been moved from the rear side, is stopped and a longitudinal central position where the slider  70  for movement, which has been moved from the front side, is stopped. That is, the slider  79  for movement is stopped at a position in a specific range defined as the neutral area. As shown in FIGS. 72 and 73, it is ideal that the rack member  17  or the main tray  8  be stopped in a state that each of the gear teeth of the second side surface gear  89  be located at a position shown by a two-dot chain line; however, it is difficult to realize such an ideal state from the viewpoint of gear mechanism. 
     For this reason, as described above, according to the disc changer apparatus  1 , the positional deviation due to backlash is adjusted by the first projection  83   a  and the second projection  85   a  provided on the cam groove portion  78  of the slider  79  for movement. 
     To be more specific, when the sub-tray  18  is moved from the disc containing position to the disc mounting position, the engagement pin  77  of the cam gear  74 , which has been moved from the starting end portion  83  to the front side circular-arc portion  84 , runs over the first projection  83   a , so that the slider  79  for movement is moved forward by an amount corresponding to the projecting amount of the first projection  83   a . As a result, the sub-tray  18 , which has been moved from the disc containing position to the disc mounting position, is moved forward by the amount corresponding to the projecting amount of the first projection  83   a , to certainly reach the disc mounting position. 
     On the other hand, when the main tray  8  is moved from the main tray pull-out position to the disc mounting position, the engagement pin  77  of the cam gear  74 , which has been moved from the rear side circular-arc portion  85  to the front side circular-arc portion  84 , runs over the second projection  85   a , so that the slider  79  for movement is moved rearward by an amount corresponding to the projecting amount of the second projection  85   a . As a result, the main tray  8 , which has been moved from the main tray pull-out position to the disc mounting position, is moved rearward by the amount corresponding to the projecting amount of the second projection  85   a , to certainly reach the disc mounting position. 
     The projecting amount of each of the first and second projections  83   a  and  85   a  is required to be equal to or more than one-half the backlash “d”. 
     According to the disc changer apparatus  1 , the relay board  91  is mounted on the back surface of the front end portion of the housing  2 , wherein the control circuit board  90  is connected to the relay board  91  via the flexible board  92  and the relay board  91  is connected to the main board, which is used for performing overall control of the acoustic equipment  100 , via another flexible printed board led from the relay board  91 . 
     Since the control circuit board  90  is connected to the main board via the relay board  91 , a vibration system generated from the base unit  24  or the like at the time of reproducing the disc-like recording medium is ended in the disc changer apparatus  1 , and is less affected by another flexible printed board led from the relay board  91  and connected to the main board. 
     FIGS. 74 and 76 are graphs showing an experimental example performed in the case where the control circuit board  90  is connected to the main board via the relay board  91 , wherein FIG. 74 shows values measured at an inner peripheral portion of a disc-like recording medium, and FIG. 76 shows values measured at an intermediate portion between the inner peripheral portion and an outer peripheral portion of the disc-like recording medium. 
     FIGS. 75 and 77 are graphs showing an experimental example performed in the case where a circuit board provided in the disc changer apparatus is directly connected to the main board provided outside the disc changer apparatus not via the relay board  91 , wherein FIG. 75 shows values measured at an inner peripheral portion of a disc-like recording medium, and FIG. 77 shows values measured at an intermediate portion between the inner peripheral portion and an outer peripheral portion of the disc-like recording medium. 
     In the figures, the ordinate designates a tracking error (deviated amount from a recording track), and the abscissa designates time. As the deviated amount on the ordinate becomes large, there occurs an inconvenience, for example, a so-called sound skip due to a tracking error. 
     As shown in FIGS. 74 to  77 , it is revealed that in the case of providing the relay board  91 , the deviated amount from the recording track becomes small, thereby optimizing the reproducing operation of signals recorded on the disc-like recording medium. 
     According to this embodiment, the sub-tray  18  in the stocker  41  is lifted up by the lift-up portions  23  so that the lowermost containing portion  41   c  is taken as a containing portion in which the next sub-tray  18  is to be contained; however, the present invention is not limited thereto. For example, the sub-tray  18  in the stocker  41  may be pushed down so that the uppermost containing portion  41   a  be taken as a containing portion in which the next sub-tray  18  is to be contained. 
     While the embodiment of the present invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.