A surface light emitting device emits light from a light emitting surface, the light being from a light source arranged on one side of the light emitting surface. On the bottom which faces the light emitting surface, a transparent light-guiding board is arranged. The board has small reflecting projections thereon. The density of the reflecting projections increases gradually from the light source. The light from the light source is reflected by the reflecting projections and emitted from the light emitting surface. Since the light from the light source is reflected toward the light emitting surface side in accordance with the density of the reflecting projections, the light is uniformly emitted from over the entire emitting surface. The reflecting projections are staggered in the direction where light is emitted from the light source, making it easy for the light to strike the staggered reflecting projections. The surface of each projection, extending from the top to the board, is preferably a curved one, or the shape of each one is preferably a cone.