To accurately detect the existence of a frame and to enhance retrieving accuracy even when the photographing system of a film is changed by deciding whether the frame exists or not based on a binarized signal obtained based on a density sensor selected by a sensor selection part.

Density signals being the outputs of 9 optical sensors 108 are separately inputted to a binarization part 110 and binarized synchronously with a sampling signal outputted by an encoder. Then, 9 binarized signals are respectively inputted to a decision part 112 and the decided result of the existence of the frame is obtained based on the outputs of the respective sensors 108. Besides, the signal of the sensor selection part 114 is also inputted to the decision part 112. By the selection part 114, optical fibers 106 whose end surfaces are positioned within the traveling locus width of the frame corresponding to the photographing system of the film and the sensors 108 connected to the fibers 106 are selected. By the decision part 112, the existence of the frame is decided according to the photographing system by selecting only the decided result of the sensor 108 selected by the selection part 114 out of 9 decided results.