PURPOSE: To prevent photometric errors owing to the differences in the reflectances of a shutter front curtain and a film without using random number patterns by so constituting a titled device that photocurrent amplification factor is changed after the shutter front curtain ends traveling.

CONSTITUTION: A changeover switch 16 is changed over to the 1st movable contact 18 side during traveling of a shutter front curtain, and therefore the electric current flowing in a capacitor 42 through an operational amplifier 24 decreases. The reflectance of the shutter front curtain is set low and differs from the reflectance of a film. Hence, the electric current which is flowing in the capacitor 42 and is integrated is made the same irrespective of traveling of the shutter front curtain. If, for example, the reflectance of the shutter front curtain is assumed to be 1/8 as compared to the reflectance of a film, the photocurrent amplification factor of the amplifier 24 is changed over in such a way that the photocurrent goes 1/8 after the shutter front curtain ends traveling. With such constitution, the photometric errors owing to the difference in the reflectances of the shutter front curtain and the film are prevented without using random number patterns.