To prevent a picture from being seized by the display of a still image by changing the luminance of an image under display by controlling a seizure prevention circuit at prescribed time.

The picture is prevented from being seized by lowering the luminance of the image under display by controlling a seizure prevention circuit 2 by the control signal of a seizure prevention control circuit 4 with a built-in timer. Succeedingly, a video signal level for one image of video signals inputted from a video signal source 1 is detected by the seizure prevention control circuit 4, the video signal level of the last image is compared with the video signal level of the next image, and their video signal level changes are discriminated. The similar operation is repeated until the presence of such a level change is discriminated and when the level change is discriminated, such an operation for seizure prevention is released. Thus, the luminance of the image under display is heightened.