PURPOSE: To decide whether the film frame has a half size or a full size, by detecting whether the notch intervals of a negative film frame is an odd or even times as much as the length of a half-size frame.

CONSTITUTION: The passing of a splicer part 3 that joined the nega films together is detected by a photoelectric detector using infrared rays. Then a notch 4 provided to each printable frame is detected, and the shifted extend of a film is counted until the next notch arrives to discriminate a half-size frame or a full-size frame. No notch is given to a defective frame, and accordingly, the film size is not always known by the notch interval. In this respect, if the notch interval is equal to the value an odd times as much as the half-size length, the film is decided as half size.