An amount of change calculated by an amount-of-change calculator (11) is stored in an amount-of-change storage (12), and an amount-of-change comparison unit (13) compares an amount of change between a frame one frame before a frame whose gradation is to be corrected and a frame before that frame. If the amount of change is larger than a predetermined value, correction value data of the frame one frame before is not used, but a correction value table of a frame before the change is chosen and read from a correction value calculator (15). If the amount of change is equal to or smaller than a predetermined value, a correction value table of the frame one frame before which did not changed much is read from the correction value calculator (15) and is written to a lookup table (16). Correction data (level data) is read from the lookup table (16) at an address and is outputted as a gradation-corrected luminance signal. In this way, based on an amount of change in a screen and according to a frame whose gradation is to be corrected, optimum correction data is chosen and gradation correction is performed, and thus optimum gradation correction can be done without a frame memory.