A surface light source device includes a light source facing a reflective surface of a reflecting member, and a light-controlling member composed of a transparent material and disposed across the light source from the reflecting member in such a manner as to face the reflective surface, the light-controlling member guiding light emitted from the light source in a predetermined direction. The light-controlling member has on a surface thereof remote from the reflective surface projections arranged on a plane. The projections have profiles of at least one kind, each having a symmetry axis or a symmetry plane. The symmetry axes or the symmetry planes of the projections are tilted at a predetermined angle with respect to a direction in which the light controlling member faces the reflecting member.