PURPOSE: To increase the quantity of light transmitted to a photoconductor and to improve the luminance of light emitted from a light diffusing transmission plate in the back light formed so that light emitted from a fluorescent discharge tube to the photoconductor is reflected by a reflecting sheet and emitted from the light diffusing transmission plate.

CONSTITUTION: The back light is equipped with the photoconductor 1 which transmits light, the diffuse transmission plate 2 which is fixed to one surface of the photoconductor 1, the reflecting sheet 3 which is fixed to the other surface of the photoconductor 1 and has a reflection pattern, the fluorescent discharge tube 5 which is arranged at one side end part of the photoconductor 1, and a reflection cover 6 which has a curved surface reflecting the light from the fluorescent discharge tube 5 by covering the fluorescent discharge tube 5. The light transmitted through the photoconductor 1 is reflected by the reflection pattern and light having luminance based upon the reflected light is emitted from the emission surface of the light diffusing transmission plate 2. A lst gap S1 formed between the fluorescent discharge tube 5 and photoconductor 1 is almost as large as a 2nd gap S2 formed between the fluorescent discharge tube 5 and curved surface and the sum of the 1st and 2nd gaps is larger than the diameter of the fluorescent discharge tube 5.