A backlight unit for use in a liquid crystal display device is disclosed. The backlight unit which may include a reflection plate; a plurality of fluorescent tubes; and a diffusion plate. The reflection plate may include a rectangular-shaped bottom plate section, four side plate sections respectively formed upright from four sides of the bottom plate section with a skew in the direction of moving away from the bottom plate section, and an edge plate section that protrudes from a tip end of each of the side plate sections toward outside thereof.