A surface light source includes a light source and an optical waveguide plate. The light source serves to emit light. The optical waveguide plate has an incident end face where the light is incident and a light exit surface where the light incident on the incident end face exits. Further, the optical waveguide plate has a refractive index n. The incident end face has a plurality of concave portions. The angle between a plane formed by the plurality of concave portions and a tangent plane of the incident end face is not more than (90−2·arcsin(1/n)) degree.