Embodiments of the present disclosure include a backlight unit and a display device using the backlight unit comprising a plurality of light emitting elements disposed on a substrate and each having a flip chip structure. A reflector is disposed between the plurality of light emitting elements and includes a plurality of grooves each having a predetermined size on an upper surface of the reflector. A transparent sheet is disposed on the reflector and the plurality of light emitting elements and includes a plurality of optical path changing patterns disposed at positions overlapping the plurality of light emitting elements on an opposite side of a surface of the transparent sheet adjacent to the plurality of light emitting elements and each having a central region thicker than an outer region.