A backlight unit comprising: a quadrilateral light guide plate 4; and a substrate 3 comprises a plurality of light-emitting diodes 2; and an inner frame 8 which surround the light guide plate 4; and an outer frame 7 which surround the inner frame 8 and the substrate 3; a plurality of rubber members 9; wherein a side of the inner frame 8 is opposite to the light-emitting diodes 2, and two corners are formed edges of the side; and the rubber member 9 is placed the each corners; and wherein the rubber member 9 comprises a cylindrical part; and wherein the cylindrical part is projected inside of the inner frame 8.