PURPOSE: To enter a proper automatic exposure state in a short time and to obtain a natural image at all times by operating a switch circuit and decreasing the time constant of an integration circuit when exposure control is switched from a manual exposure mode to an automatic exposure mode.

CONSTITUTION: Associatively with switching from a manual exposure correction mode to an automatic exposure correction mode, a system control circuit 9a turns on the switch circuit 14 for a certain time. When the circuit 14 is on, the output of an operational amplifier 8 is a reference voltage Vref without being affected by the video signal on its inverted terminal side. Therefore, when the manual exposure correction mode is switched to the automatic exposure correction mode, feedback is provided almost in a proper exposure state and an iris 2 becomes stable in a proper state in a short time without being affected by the time constant of the integration circuit Sa of the amplifier 8, so that an invariably natural image is obtained.