A display device includes an image display panel, a light source unit, and a signal processing unit. The tentative expansion coefficient calculating unit calculates a tentative expansion coefficient. The tentative index value calculating unit calculates a tentative index value serving as an index of the irradiation amount of light based on the tentative expansion coefficient. The low-saturation pixel detecting unit detects low-saturation pixels in a certain region on an image display surface. The light irradiation amount calculating unit calculates a comparative light irradiation amount based on a detection by the low-saturation pixel detecting unit, a display quality maintenance reference value at which the display quality of colors displayed by the low-saturation pixels is maintained, and an index value calculated based on the tentative index value and calculates, based on the comparative light irradiation amount, a light irradiation amount serving as the irradiation amount of light.