PURPOSE: To make it possible to obtain a proper exposure at all times by detecting a mechanical error which occurs when a diaphragm mechanism is controlled, utilizing the information of diaphragm value actually stopped down, and counting for correcting a shutter second time by a proper or improper quantity of this diaphragm value.

CONSTITUTION: In case the diaphragm control of exposure time priority, film sensitivity value set by SW4 and brightness value of object from photo-detector element 1 via amplifier 2 are added in the addition counter 3 to memorize it in the latch 5. Proper diaphragm value F is counted from the added value and exposure time value set by SW8 in the diaphragm value count circuit 6, whose output causes diaphragm value display meter 9 to swing. Indicator needle of the meter 9 is suppressed synchronously with the release operation, and diaphragm mechanism 11 is stopped down by diaphragm control mechanism 10 with the indicated value as its reference. Information of diaphragm value F' which may contain the error acturally stopped down is detected by SW12 which sets diaphragm value in coupling with the diapragm mechanism 11. When timing SW ST is made OFF by this detection, input 7b is subtracted from input 7A per unit time one pulse in the subtraction counter based on the information of diaphragm value F' given to input 7B. Thus the corrected exposure time when the output becomes zero is obtained.