PURPOSE: To detect suitably and economically an abnormality by comparing a reference picture with the newest picture data and activating an external recording device and an alarming device only when the change in pictures more than a reference is detected.

CONSTITUTION: A control circuit 18 supplies the newest video signal outputted from an A/D converting circuit 20 to a picture memory 22. A picture processor 30 processes the newest video signal and the reference video signal and checks always whether or not the difference is a preset reference by comparing the both. If the change more than the reference is detected, the external recording device 32 is driven to record the video output of a television camera 10 and an alarm device 34 is operated to inform the supervisor the operation.