Patent ID: 6981791

Claim:
A surface light source device comprising: a light-emitting element which generates light; a light guide plate which has a plate-like shape and comprises an end face and two opposing plate surfaces, wherein light emitted from the light-emitting element is incident on the end face, and the light guide plate causes the light to be reflected between the plate surfaces to guide the light along the plate surfaces, causes the light to emerge from the two plate surfaces, and transmits light incident on one plate surface toward the other plate surface; a first optical element which is placed on a side of a first said plate surface side of the light guide plate, and which transmits a part of light emerging from the first plate surface of the light guide plate toward a front side, and returns the remaining light to a rear side; and a second optical element which is placed on a side of a second said plate surface of the light guide plate, and which transmits at least a part of light emerging from the second plate surface of the light guide plate; and wherein the light guide plate includes a diffusion surface at the second plate surface to diffuse internally reflected light.