PURPOSE: To enhance the reliability of interchanging operations and reduce the cost by mechanically accomplishing the interchanging operations of forward and backward movements of a tray without the use of a punger.

CONSTITUTION: In case a tray 20 is moved forward to this side to interchange slide frames 19, a forward operating button 51 is depressed under the condition, in which the slide frames 19 are charged into a projecting position. Then, a plunger 8 is energized so that the rotations of a motor 1 are transmitted to a large gear 12. By the rotations of the large gear 12, a push arm 18, a return arm 21 and a slide arm 17 are moved leftwardly to accommodated the slide frames 19 in the tray 20. After that, a moving lever 25 turns a rotary disc 32 counter-clockwise through an engagement pin 40. As a result, a frame advancing gear 31 is turned clockwise, and a forward gear 28 is also turned clockwise so that the tray 20 is advanced for one of the slide frames 19 through the rack gear 28.