An augmented reality head-up display (AR HUD) apparatus is provided. A backlight unit (BLU) for an AR HUD includes a light emitting diode (LED) array including a plurality of LEDs, a primary lens array configured to primarily concentrate light output by the plurality of LEDs, a secondary lens array configured to secondarily concentrate light incident through the primary lens array, and a side reflector configured to reflect light traveling toward a side surface above the secondary lens array among light incident through the secondary lens array.