Light which tries to enter a diffuser plate 3 at an angle which exceeds an angle at which a percentage of reflected light increases rapidly (that is, the incidence angle θ=70 degrees) is all reflected by a reflecting surface 21 and then enters the diffuser plate 3. Therefore, a pseudo light source is formed by light which was collected near a connection point between adjacent reflecting surfaces 21 out of the emitted light of the discharge lamps 1. So, the brightness between the adjacent discharge lamps 1 is increased, and it is possible to reduce unevenness in brightness. Furthermore, since the discharge lamp 1 is housed inside the reflecting surface 21 whose cross-sectional shape is a parabola, it is possible to reduce the distance between a reflecting plate 2 and the diffuser plate 3, as compared with the prior art, and to reduce the thickness dimension in the anteroposterior direction.