A backlight unit, in which an incident surface of a light-guiding plate is formed in a shape of a curve, or a curve-shaped structure is formed in a housing to improve the light efficiency. The backlight unit includes a light source emitting light; a housing surrounding the light source; a light-guiding plate guiding the light emitted from the light source to an LCD panel, wherein the light-guiding plate has an incident surface formed in a shape of a curve; and a reflective sheet formed under the light-guiding plate.