PURPOSE: To quicken the start of photometry and range-finding and to increase the number of photographing times per unit time in the case of consecutive photographing while tracking a subject in autofocusing by making bound time when a mirror member collides with a mirror receiving member and bounds shorter than the bound time in a state where the mirror receiving member is fixed.

CONSTITUTION: When a main mirror 1 descends, a pin 25 collides with a main mirror holding frame 2. Since a weight 27 is attached between a member on the main mirror 1 side and a member on a main mirror receiver 22 side, the member on the mirror 1 side hardly stops after the collision, and the member on the mirror receiver 22 side is rotated clockwise around a shaft 18. Soon, the member on the mirror receiver 22 side stops rotating clockwise, and starts rotating counterclockwise by the pressing force of a spring 26. Then, the pin 25 collides with the main mirror holding frame 2 for the second time. At such a time, the kinetic energy of the member on the mirror receiver 22 side is completely dissipated, and the member on the mirror 1 side hardly bounds.