PURPOSE: To obtain an easy-to-use program shutter by varying a photodetection output characteristic for automatic exposure control on the basis of a signal from an electric signal generating means which is associated operatively with a diaphragm.

CONSTITUTION: Photodetecting elements PC having different resistance values R1 and R2 are switched through the detection part switch SSW1 of an exposure driving part 4, and the switch SSW1 is operated by a switch operating projection provided to an exposure driving part 47. A switch PSW2 on the side of a photodetecting element PC(R2) turns on at time t0 when the shutter starts opening, and the switch PSW1 on the side of a photodetecting element PC(R1) turns on at time t1 while the PSW2 turns off. The switch PSW1 turns on and the PSW2 turns off at time t3. A capacitor C for photometric information storage is charged over said switching and a closure indication is generated at time t4 when a reference voltage becomes equal to the charging voltage to the capacitor C, closing the shutter.