PURPOSE: To obtain bright, and thin back illuminator of a uniform brightness distribution inexpensively by arranging a pair of line light sources on both sides and providing a light reflecting plane with high reflectance between both light sources.

CONSTITUTION: A lamp house 1 is a mold made of ABS resin as raw material, and a pair of line light sources 2 and 2 are arranged not right under the illuminated surface 3 of its inside but on both sides. The light reflection plane 4 is formed between the line light sources 2 and 2 by using the internal surface of the lamp house 1. In order to form the light reflection plane 4, after undercoating on the surface, it is coated with metal of high light reflectance such as aluminum, etc., by evaporation method, etc., after its front surface is undercoated and topcoating is applied thereon as a surface protecting layer. Thus, the light reflecting plane 4 becomes the perfect mirror surface, and light beams which the line light sources 2 and 2 have emitted are reflected efficiently to irradiate the illuminated plane 3. Therefore, a brightness distribution becomes uniform and the device is made thin.