PURPOSE: To accurately perform exposure suitable for all shutter speeds from a low speed side to a high speed side whatever diaphragm aperture is set.

CONSTITUTION: A microcomputer 80 obtains theoretical time corresponding to a set diaphragm value and set shutter speed. The theoretical time is finely adjusted(corrected) basing on a value in accordance with the set shutter speed, and the shutter is opened/closed only for the time related to the correction, so that the appropriate exposure suitable for the set diaphragm aperture and the set shutter speed is always performed.