A backlight unit which prevents an initial driving malfunction is disclosed. The backlight unit includes: a bottom cover opened upwardly; a reflective sheet disposed in the inner surface of the bottom cover; a plurality of lamps arranged in a fixed interval on the reflective sheet; a driver disposed on the rear surface of the bottom cover; an auxiliary light source loaded on the driver; a first hole formed in a region of the bottom cover opposite to the auxiliary light source; and a hole region, on the reflective sheet, including one of plural micro-penetration holes and plural slit holes and opposite the first hole on the reflective sheet.