PURPOSE: To prevent the shift of a formed film cylinder, film detachment and film cutting, by detecting a discrimination mark such as a seamed part or a terminal end part having difference in light perviousness by photoelectric tube detection apparatuses different in sensitivity arranged in a film running process.

CONSTITUTION: When a film 2a runs to the position of photoelectric tube detection apparatuses from a wound roll 1a while the adhesive place of the tape 9a or 9b of the film 2a is withdrawn, a detection signal is outputted from the high sensitivity photoelectric tube detection apparatus 3a in the case of the tape 9a high in light perviousness but the low sensitivity photoelectric tube detection apparatus 3b can not detect the tape 9a and the detection signal is not issued from said apparatus 3b. In the tape 9b low in light perviousness, detection signals are issued from both photoelectric tube detection apparatuses 3a, 3b. Therefore, when one of the tapes 9a, 9b is set to the discrimination mark of a seamed part while the other is set to that of a terminal end part, the seamed part and the terminal end part can be certainly and separately detected.