PURPOSE: To make possible easy and sure reading by rotating a disc which indicates the numbers of the frames of a tray each time when the tray containing plural slide frames is moved by one frame thereby digitally displaying the tray frame number in a slide projector.

CONSTITUTION: When a tray 4 is set in a frame feed operation state, a plunger 18 is energized. Slide frame exchange mechanism operates and a push arm 16 moves rightward. When it comes to the position of not interfering the movement of the tray 4, a frame feed gear 7 is rotated clockwise for one frame by the frame feed mechanism, causing the tray 4 to be moved one frame rightward by intermeshing of the rack part 6 and frame feed gear 7. As a result, the slide frame 5 of tray number 1 is loaded from the inside of the tray 4 into the projection position by the operation of the push arm 16. As the frame feed gear 7 rotates, a display gear 11 is rotated clockwise by way of an auxiliary gear 9 and intermediate gear 10. This causes the disc 13 to rotate as well and the tray number 1 is displayed in the display window 3 of the main unit 1. The operation of the frame feed causes the disc 13 to rotate, thus subsequently displaying the numbers corresponding to the tray numbers in the display window 3.