To make the intensity of light emission of a surface light source uniform.

The surface light source includes a light source and a light guide plate. A light emitted from the light source is incident from an incident end face of the light guide plate and is output from an output surface of the light guide plate. The incident end face has a plurality of recessed parts. The refractive index of the light guide plate is n. An angle formed by a plane of the plurality of recessed parts and a tangential plane of the incident end face is not larger than (90-2arcsin (1/n)) degrees.