PURPOSE: To bring aperture value automatically and surely to the specified value in cooperation with the elevation of a mirror with a simple mechanism by interlocking an aperture drive lever to a mirror elevating lever.

CONSTITUTION: When the engagement by a hook lever 9 is released by shutter release, a mirror elevating lever 7 is turned clockwise about the pin 10 of an aperture drive lever 4 by the elastic force of a spring 11, by which a mirror 8 is moved to kick up the mirror. On the other hand, the lever 4 is turned about the pin 10 by the elastic force of a spring 12 cooperatively with the turning of the lever 7 until it contacts the contact surface 16 of a cam 17 through a turning motor 18 according to photometry, by which the aperture rod 6 of the lens 5 is moved upward and the specified aperture value is automatically and surely set by the simple mechanism.