PURPOSE: To prevent the flicker of a picture, to obtain a corrected output with gradation, and to prevent the generation of black painting-out or white painting- out by detecting and correcting the mean luminance level of a video signal input, switching a gamma correcting characteristic according to the corrected mean luminance level, and correcting the video signal input.

CONSTITUTION: The mean luminance level of the video signal input in a prescribed period is detected by an APL detecting circuit 3, a detected signal from the APL detecting circuit 3 is converted into APL data by an A/D converter 4, and the APL data are corrected by a stabilizing circuit 7 so that the switching of the gamma correcting characteristic can be stabilized. The signal and a signal obtained by converting the video signal input into a digital signal by an A/D converter 2 are inputted to a ROM 5 for gamma correction as address signals. Then, the plural gamma correcting characteristics preliminarily stored in the ROM 5 for gamma correction are switched by the corrected APL data, and the video signal input is gamma-corrected and outputted.