PURPOSE: To make it possible to realize a reduction in thickness and excellent illumination efficiency by irradiating the observation surface of an object to be illuminated with the light scattered by light scattering parts from the rear surface of a light transmission plate.

CONSTITUTION: The incident light on the light transmission plate 3 from a light source 1 progresses while repeating reflection in the light transmission plate 3. This light is partly scattered by the scattering parts 4 formed on the front surface side of the light transmission plate 3. Of the light further scattered downward, the light having a steep angle with the rear surface of the light transmission plate 3 deviates from a total reflection condition and is emitted from the rear surface of the light transmission plate 3. The object 6 to be illuminated arranged below an illumination device is efficiently illuminated. On the other hand, the light is usually scattered to the front surface side of the light transmission plate 3 as well from the scattering parts 4 and, therefore, light shielding parts 5 are arranged on the front surfaces (observation surfaces) of the scattering parts to provide a structure to prohibit direct viewing of the scattered light. Then, an observer eventually sees only the light reflected by the object 6 to be illuminated among the scattered light rays as the observation light from the spacings between the scattering parts 4. The improvement in the illumination efficiency and the uniformity of display are thus assured.