A surface light source device has a light-conductor plate operable to conduct light inside and allows the light to exit at a light-exit surface to outside, a light source that is small compared to a width of the light-conductor plate, having a first surface arranged opposite to a light incident surface of the light-conductor plate, and a second surface opposite the first surface, and a fixture having fit pieces engaged on fit areas formed on the light conductor plate, an abutment piece urged to a push area formed on the second surface of the light source, and clamp pieces urged to clamp steps formed on the light source. The abutment piece urges the push area to the light incident surface by an elastic reactive force generated by elastic deformation of the fixture between the fixture and the abutment piece.