An input video signal is corrected based on a gradation correction curve. Generated first is histogram data which indicates distribution of each of a plurality of levels at which a luminance signal component of the input video signal is divided from the lowest to the highest luminance level per specific unit of image. Produced next is at least a first gain based on the distribution of the histogram data. At least the first gain and the histogram data are processed to produce a plural number of data for a gradation correction curve. The gradation correction curve is generated based on the plural number of data. The input video signal is then corrected based on the gradation correction curve.