An illumination device includes a display panel including a first surface on which an image is displayed, a second surface opposite to the first surface, display pixels interposed between the first surface and the second surface, and a transmitting window interposed between the first surface and the second surface. The illumination device further includes a light source disposed on a side of the second surface of the display panel, and emitting light toward the second surface, and a light transmitter interposed between the light source and the display panel, and transmitting the emitted light to the transmitting window, the transmitted light being incident on the second surface of the display panel and being transmitted through the transmitting window toward the first surface of the display panel. The illumination device further includes a diffuser diffusing the light transmitted through the transmitting window.