A display device is provided with an illuminance sensor (30) which detects the illuminance of a surrounding environment, an input average brightness detection circuit (21) which detects the average brightness of an input image, a frame insertion control circuit (24) which generates a gray image frame and inserts the generated gray image frame between an input image frame and an input image frame inputted next, and an insertion brightness level generation circuit (22) which determines the brightness of the gray image frame according to the illuminance detected by the illuminance sensor (30) and the average brightness of the input image detected by the input average brightness detection circuit (21).