To efficiently use external light and to enhance luminance by providing a light transmission plate arranged on the side surface of a device and having the light receiving surface of the external light on its side surface, leading the external light incident on its light receiving surface through the light transmission plate and irradiating it from its one end onto the panel surface of the device.

This device consists of a device main body 1 and the light transmission plate 2 arranged on the side surface integrally with the device main body 1 so that the end part 5 of the light transmission plate 2 is placed on a display surface side of its one end. Although the external light 6 is made incident directly on the display surface of the device main body 1 also, the external light 6 incident on the light receiving surface 3 of the light transmission plate 2 enters from a groove or a notched part 4 the inside of the light transmission plate 2, and a part of it is led to the end part 5 of the light transmission plate 2 by total reflection to go out to the outside from the end part 5. By obliquely tilting the surface of the end part 5 as shown in the figure, the majority of the light emitted from the end part 5 to the outside is made incident on the display surface side of the device main body 1. Thus, the component incident from the light receiving surface 3 and emitted from the end part 5 through the light emission plate 2 is added to the display surface of the device main body 1 in addition to the directly incident external light component.