To reduce temporary disorder of exposure when an ND filter is put in and out from the optical path of a lens and to reduce the time required for returning to proper exposure.

A luminance signal obtained by detecting a video signal photographed by a CCD 504 by a luminance signal detection circuit 507 is sent to an iris control signal arithmetic circuit 511 to be compared with a reference value, and such an iris control signal as makes the luminance signal constant is calculated. In the case, a control signal for operating an iris 503 fast and a control signal for operating the iris 503 slowly are generated, and the control signal for operating the iris 503 slowly is used normally. When a user turns on/off the ND filter 502, an iris fast control part 512 is selected to accelerate response of iris control to reduce a time required until exposure is optimized to reduce a variance in luminance of the video signal to speedily return to optimum exposure.

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