To reduce the difference of brightness between the center and the periphery of an image plane in the vicinity of telephoto end where the fluctuation of the brightness of the image plane caused synchronously with the correction of camera shake is conspicuous and to obtain a high-quality and easy-to-view image by restricting the diameter of the opening of a diaphragm for controlling the quantity of passing luminous flux in accordance with a focal distance in a variable power optical system for correcting camera shake.

A microcomputer 16 moves moving frames 11 and 8 in an optical axis direction by a focus motor driving circuit 19 and a zoom motor driving circuit 20 while monitoring outputs from a focus reset circuit 17 and a zoom reset circuit 18. When the moving frame comes to a set position, the number of the succeeding driving steps of a stepping motor is counted in the microcomputer 16, so that the absolute position of each lens group is known and focal distance information is obtained. A driving circuit 21 controls the diameter of the opening of the diaphragm, based on the brightness information (b) of a video signal fetched in the microcomputer 16. The diameter of the opening of the diaphragm is restricted in accordance with the focal distance in controlling the diaphragm and the difference of the brightness of the center part and the peripheral part of the image plane is kept small.