A flash detection unit calculates a line average luminance of each line of the current screen of image data and a screen average luminance of a past screen at least one screen before the current screen and compares the calculated line average luminance with the calculated screen average luminance to detect whether the current screen includes a line of high luminance due to a flash. A holding unit holds the past screen of the image data. A flash correction unit, if it is detected that some lines of the current screen have high luminance, replaces the lines having high luminance in the current screen with corresponding lines of the past screen held in the holding unit to correct the image data.