PURPOSE: To enable the adequate aperture speed to be automatically obtained along with progression of operation mode in each photographing mode by selecting the driving frequency of a stepping motor by a gate circuit and digitally controlling mode operations.

CONSTITUTION: The quantity of light passing through an aperture mechanism 1 controlled by a stepping motor 2 is detected by a photo detecting means 3. In the oscillation circuit 4 which generates repetitive pulse trains of plural different frequencies for letting the stepping motor 2 run at different speeds, one pulse train is selected from the plural pulse trains by a gate circuit 5 which is controlled by the output of a photo detecting means 3 or the control signal emitted along with progression of each operation mode such as lap, fade, etc. A motor control circuit 24 drives the stepping motor 2 bt receiving the output from the gate circuit 7.