To prevent a diaphragm plate from being switched even when the subject light quantity is changed in the midst of exposure.

The diaphragm is switched by moving the diaphragm plate by means of a solenoid 51. A diaphragm control circuit is equipped with a solar battery 26 outputting a light quantity signal in accordance with the subject light quantity and a switching transistor 74 actuating the solenoid 51 when the light quantity signal is equal to or above a specified value. A transistor 76 functions to supply a base current to the transistor 74 from a power source battery 39 in order to maintain the actuated state of the solenoid 51. A stopping switch 63 functions to stop the actuation of the battery 26. A main switch 62 is turned on by half-depressing a shutter button and, on the other hand, the switch 63 is turned off by fully depressing the shutter button. Thus, even when the subject light quantity is changed in the midst of exposure, the state of the solenoid 51 is maintained.