A surface light source device includes a light source body, a partition member, an isolating member and a voltage applying part. The light source body has an internal space into which discharge gas is injected. The partition wall divides the internal space into discharge spaces. The partition wall has a connection hole that connects the discharge spaces with each other. The isolating member is disposed such that the isolating member corresponds to the connection hole. The isolating member seals the connection hole to isolate the discharge spaces from each other. The voltage applying part induces discharge of the discharge gas in the discharge spaces. Thus, current drift is prevented.