To prevent flicker in a photographed image by prohibiting auto-iris control of an on-vehicle camera when a vehicle body lamp is flashed.

A controller 11 is constituted with a microcomputer and its peripheral parts, a control program is executed and auto-iris control is performed. When an outside vehicle monitoring switch 3 is turned on, the control program is executed by the controller 11 at every specified interval of time. It is confirmed whether a turn signal switch 4 or 5 or a hazard switch 6 is turned on and, when any one is switched on, the auto-iris control of a CCD camera 1 is prohibited and a charge accumulative time is fixed to a constant value. When all the turn signal lamps 4 and 5 and the hazard switch 6 are turned off, the auto-iris control is permitted, photometry is performed by a photometry circuit of the CCD camera 1 and the charge accumulative time of a CCD imaging device is set in accordance with a photometry value.