A display device using an external light, includes: a main body including a light source; at least one auxiliary light source; and a display unit. The display unit includes a first end hinged with the main body such that the display unit can be opened and closed. The display unit also includes a transmissive display panel which forms an image. When the display unit is open, external light is incident onto the display panel and light from the at least one auxiliary light source is selectively supplied to the display panel.