A backlight unit of a display apparatus, the backlight unit includes a light source unit disposed on at least one edge of a display panel; and a light guide plate disposed at rear of the display panel. The light guide plate includes a first pattern part including a plurality of first pattern lines formed on a lower surface of the light guide plate, and which extend perpendicularly to a transmission direction of the radiated light, and which totally reflect the radiated light to an upper surface of the light guide plate, and a second pattern part including a plurality of second pattern lines formed on the upper surface of the light guide plate, and which extend parallel with the transmission direction of the radiated light, and which guide light transmitted in the light guide plate to travel and exit along the second pattern lines.