PURPOSE: To achieve the improvement in correction effect with each interchangeable lens by adjusting either of the finder or photographing optical system on the body side through the use of the corecting means provided to each interchangeable lens.

CONSTITUTION: For a lens which requires adjustment by retreating a mirror box 8, a mirror-box-retreating cam 21 is provided as a correcting means on the flange face B of said lens so as to push and move a moving pin 10. For a lens which requires adjustment by advancing the mirror box 8, a release cam 22 is provided in addition to the cam 21 and a stopper release pin 18 is pushed and moved by the cam 22 to let a reference position stopper 20 retreat from the front end face of the mirror box 8 and therefore the mirror box advances and its movement is determined by the position of the moving pin 10. In this way, the maximum focus may be obtained with each of the interchangeable lenses.