A flat panel display device includes: a first display unit, a second display unit, and a third display unit. The first display unit comprises a (1-1)-th surface facing a (1-2)-th surface, and is configured to display an image on the (1-1)-th surface and enable external light to transmit from the (1-2)-th surface to the (1-1)-th surface. The second display unit comprises a (2-1)-th surface facing a (2-2)-th surface, and is configured to display an image on the (2-1)-th surface and enable external light to transmit from the (2-2)-th surface to the (2-1)-th surface. The third display unit comprises a (3-1)-th surface facing a (3-2)-th surface, and is configured to display an image on the (3-1)-th surface. The third display unit is disposed between the first display unit and the second display unit.