A multifunctional-type backlight unit, including a light guiding plate having a first incident/exit surface and a second incident/exit surface which are capable of receiving and emitting light, a light emitting device disposed to face the first incident/exit surface and configured to supply light to the first incident/exit surface, and a light receiving device disposed to face the first incident/exit surface and configured to receive light emitted from the first incident/exit surface, the light guiding plate being configured so that the light emitted from the light emitting device enters the light guiding plate, passes through the light guiding plate, and is emitted from the second incident/exit surface, and the light guiding plate being configured so that the light which enters the second incident/exit surface, passes through the light guiding plate emits from the first incident/exit surface is received by the light receiving device.