A surface light source device includes a lamp body, a space dividing member, a discharge gas supplying member and a voltage applying part. The lamp body includes a flat shaped space and a fluorescent layer disposed in the flat shaped space to convert an invisible light into a visible light. The space dividing member divides the flat shaped space into a plurality of discharge spaces. The discharge gas supplying member is disposed to pass through the space dividing member and is fixed to the space dividing member, and supplies the discharge spaces with a discharge gas that generates the invisible light. The voltage applying part applies a discharge voltage to the discharge gas. Therefore, the lifetime of the surface light source device generating a planar light is increased, and the luminance of the light becomes uniform so that the display quality of an image is improved.