PURPOSE: To efficiently monitor plural monitoring places only with one monitor by outputting an image signal and an alarm signal for a video camera by using a level signal outputted from the camera in order to execute automatic iris adjustment.

CONSTITUTION: A level signal 21 outputted from a video camera part 1 based upon the lightness of a subject is A/D converted at a prescribed time interval and the converted digital data are stored in a storage part 13 to calculate a mean value. The calculated value is compared a mean value obtained just before and a difference between both mean values is found out and whether the difference is included within a prescribed allowable range or not is checked. A control part 15 outputs a gate control signal 22 based upon a checked result to control the output of a video signal 20. The control part 15 simultaneously outputs an alarm signal 23 also. The signal 20 is connected to a monitor display, and at the time of generating abnormality, a buzzer or the like is driven by means of the signal 23 and an image obtained by photographing the abnormality is displayed on a monitor display.