PURPOSE: To control an aperture accurately by arranging a detecting means which detect the extent of operation of an aperture operating mechanism and converts it to an electric signal so that the extent of driving from the start position of a driving system is detected.

CONSTITUTION: Since an aperture driving lever 14 is rotated clockwise by clockwise turning of a charge lever 54, the aperture driving lever 14 is pushed clockwise, and an engaging end 16a of an engaging/disengaging lever 16 is engaged with an engaging groove 18a of a sector gear 18 to couple the sector gear 18 to the aperture driving lever 4. The charge lever 54 is turned clockwise furthermore thereafter while pushing the aperture driving lever 14, and as the result, a pin 14b pushes the sector gear 18, and a transmission gear 24 is turned in the direction opposite to an arrow so that a notched end face 22c is separated from an arm part 10a of a member 10 to be transmitted whose turning is already stopped, and an overcharge spring 31 is deformed. This over charge driving of the aperture driving system is terminated when the sector gear 18 is brought into contact with a stopper 50. Thus, accurate aperture control is possible even near full aperture.