Gray level data of boundary pixels that are adjacent to a block boundary in a photoelectric conversion section is stored. Then, a cumulative histogram regarding the number of pixels for different gray levels is produced based on the stored gray level data separately for each block, and a data table representing the correspondence between each gray level before correction and that after correction for the block to be corrected is produced so as to reduce the difference between the cumulative histograms. The data table is stored in a correction data RAM. By using the data table, the outputs of the block to be corrected are non-linearly corrected for different gray levels.