A surface light source device includes a light source body having an internal space. A partition wall is disposed in the internal space of the light source body to divide the internal space into a plurality of discharge spaces. The partition wall has end portions that make contact with inner surface of the light source body. The partition wall has a throughhole, through which the discharge spaces are connected to each other. The light source body includes a voltage applying part that applies a voltage to the discharge space to generate plasma in the discharge space. A barrier is disposed adjacent to the throughhole to restrict a flow of the plasma generated from a discharge gas through the throughhole. The barrier screens the throughhole to restrict the flow of the plasma through the throughhole. Therefore, uniformity of luminance of the surface light source device is improved.