To attach a background display with a simple structure by fixing a light guide plate and a reflection plate holding a displaying matter having a specifically designed shape disposed in between.

In a surface light source device, because a background display can be performed by disposing a displaying matter having a specified shape made of a double-sided adhesive tape between a light guide plate 4 and a reflection plate 5 and by reflecting light from a light source 6 with the displaying matter, the problem can be solved with a simple structure and at a low cost. Furthermore, the background display can be made more conspicuous by mixing a fluorescent material or a light absorbing material in the displaying matter.