PURPOSE: To display the same video with the real scene difficult to detect, by outputting the bearing signal synchronous to the sweep signal only while the thickness control signal of random long time pulse is outputted and correlating to the background noise at every sweeping.

CONSTITUTION: Bearing synchronizing signal is generated by a bearing synchronizing signal generating circuit 8 synchronizing with one period of sweep signal from a sweep control part 1 only while the random long time pulse is generated from a thickness control signal generating circuit 7 and a gate 10 is opened. Voltage application to a synthesis circuit 6 of random period noise signal from a noise width signal generating circuit 9 through the gate 10 is controlled. Hereby, display in accordance with the target video signal from a target video generating part 4 and overlapped background noise video signal which is correlated with n-th rotation and n+1-th rotation of the sweep generated by the random period, is displayed on a cathode-ray tube 2. Accordingly, difficulty of detection of a target video 11 can be resembled the real scene.