As to an image signal of a solid-state image pickup device, an average value calculating unit calculates average values of pixel values of individual color components constituting an image of each frame. A gain calculating unit calculates, for the number of frames in one cycle of flicker generation, maximum values of the average values of the pixel values of the individual color components of the image, which average values are calculated by the average value calculating unit; calculates, according to the maximum values, gains for adjusting to a maximum range the average values of the pixel values of the individual color components constituting other images; and outputs the gains as gains of the individual color components to be supplied to a signal amplifying unit. The signal amplifying unit amplifies all pixels of color components of the image according to the gains of the individual color components supplied.