PURPOSE: To suppress the temperature rise of ballasts by displacing the ballasts on the tip side of lamps at the opposite position to bases, and arranging two faces connected at a right angle along the longitudinal direction of the ballasts in face contact with the top plate section of a chassis and side plate sections connected perpendicularly to it respectively.

CONSTITUTION: Ballasts 20 are displaced on the tip side of lamps at the opposite position to bases 18a of fluorescent lamps 18, and they are separately displaced on the right and left side plate sections 13, 14 side of a chassis 11. Upper faces of the ballasts 20 and one-side faces connected to them at a right angle are brought into face contact with the top plate section 12 of the chassis 11 and side plate sections 13, 14 respectively. The transfer of the high heat generated at base portions to the ballasts 20 can be reduced, and the heat conduction area from the ballasts 20 to the chassis 11 can be largely secured. The ambient temperature of the ballasts 20 is reduced, the heat radiating property of the ballasts 20 can be improved, and the temperature rise of the ballasts 20 can be reduced.