PURPOSE: To prevent respective projections from being visible from an out-going surface even when a light transmission body is formed thin and to make the light transmission body passible to be made thin by forming plural projections projecting to the outside and whose sectional shape is a nearly semi-circular shape on the bottom surface of the light transmission body.

CONSTITUTION: Plural semi-spherical shaped projections 16 projecting to the outside are formed overall on the bottom surface 13b of the light transmission body 13. The density of these semi-spherical shaped projections 16 is formed so as to become denser gradually from a pair of left and right fluorescent lamps 14a, 14b. The incident beams from the left and right ends of the light transmission body 13 propagating to central part are refracted by respective semi-spherical shaped projections 16 and emitted to the outside and reflected irregularly by a reflection sheet 15. Then, almost all of the reflected beams are made incident on the inside of the light transmission body 13 again from the bottom surface 13b of the body 13, and the incident beams on the outgoing surface 13a at a crtical angle or below are emitted to the outside from the outgoing surface 13a. Thus, since the peripheral parts of respective semi-spherical shaped projections 16 are bright when respective semi-spherical shaped projections 16 are seen from the outgoing surface 13a of the light transmission body 13, the shapes of respective semi-spherical shaped projections 16 are faded and hard to be visible from the outgoing surface 13a.