PURPOSE: To make a unit thin and to reduce the number of assembling stages.

CONSTITUTION: This backlight unit 2 has such structure that a diffusing plate 7 is provided on the upper surface of a light transmission plate 5, a fluorescent tube 8 is provided on one end side of the plate 5 and a reflection film 9 is provided over the outer peripheral surface of the fluorescent tube 8 and the lower surface of the plate 5. In such a case, since light is prevented from being leaked from the lower surface of the plate 5 by the comparatively thin reflection film 9, the unit 2 is thinned in comparison with the case that an independent comparatively thick reflector is used, and the number of the assembling stages is reduced.