PURPOSE: To detect the retrieval end of retrireal blocks readily and surely by forming the final material of the retrieval material blocks such as of slides or the like to special one or blank frame.

CONSTITUTION: When a desired slide block is selected by operating a selection button 6, an FF 11 is set and a pulse motor is run by way of a delay circuit 18, matrix circuit 7 and comparator 8 or other, whereby the searching of the selected slide block is accomplished. Next, when the slide frame moved by a changer arm is detected with a detection switch 5, a timer 25 of the time longer than the timer time corresponding to the projection time of a timer 24 starts actuating and when it times out, an OR circuit 19 opens, causing the slide frames to be subsequently retrieved by the pulse motor. The final slide frame of the block has been formed to a special frame or blank frame or the like, hence the switch 5 does not produce any detection output and the timer 25 is disabled.