A backlight unit including a light guide panel which has opposite upper and lower faces, and guides light, introduced into an inside thereof, between the upper and lower faces through internal reflection, and a prism sheet which collects and transmits the light, introduced from the light guide panel, and has, on its surface, a plurality of prism patterns, each having a first main inclined face, to which light introduced from the light guide panel is incident, a second main inclined face having a curvature or a plane which reflects light incident from the first main inclined face, and two auxiliary inclined faces which are opposite to each other between the first and second main inclined faces, and define a side face of the prism pattern.