A display device has a light unit including a light source, and a display panel, which the rear surface of the display panel has transmissive. The display device has a first display mode of turning ON the light source and displaying a color image in a display region of the display panel, and a second display mode of turning OFF the light source and displaying a transmitted light image including a transmissive region in the display region. The display device detects whether or not a observer of the display device exists around and switches into the second display mode upon detection of the observer.