PURPOSE: To use a diffusion plate as a uniform surface light source and to make the brightness of a display constant by making light from a fluorescent lamp incident from the reverse surface of liquid crystal by the diffusion plate and a mirror surface and curving the mirror surface distance from the light source according to the length of the fluorescent lamp.

CONSTITUTION: The rays of light inputted from the fluorescent lamp 1 to the diffusion plate 2 are reflected repeatedly by the mirror surface 3 surrounding the diffusion plate and inputted at right angles from the reverse side of the liquid crystal 4 as the surface light source. The part of the mirror surface 3 distant from the light source is curved according to the length of the fluorescent lamp, so primary reflected rays of light are reflected to right and left without being converged on the center of the diffusion plate 2 and becomes the uniform surface light source to make the brightness of the liquid crystal display constant.