PURPOSE: To obtain the correct exposure second time free from any exposure error by continuously correcting the change in the photometric quantity based on the difference in the reflectance of a shutter front curtain plane and film plane by the reactance element cooperating with the travel of the front curtain.

CONSTITUTION: When the shutter is released, the reflected light incident from the subject through the taking lens falls onto the front curtain where the shutter begins to open and the film plane which has begun to exposure. By reflected by this, it is received in a photoelectric transducer D and is converted to photo current. This photo current flows to a variable capacitor Cv and is charged as integrating voltage Vcc. The output of an operation amplifier OP1 is compared with decision voltage VRF in an operational amplifier OP2. When the voltage Vc increases, the magnet 18 goes OFF to close the rear curtain. If in this case the capacity of Cv is changed in cooperation with the travel of the front curtain, the voltage Vc changes like the straight line F, thereby enabling the prevention of the occurrence of exposure error.