A backlight unit includes a light source which generates light, a light guide plate which guides the light substantially in an upward direction, a first frame member which holds the light source and diffuses the light traveling substantially in the upward direction between the light source and the light guide plate, a second frame member which holds the light guide plate, a third frame member which holds the light guide plate, a reflective plate disposed under the light guide plate and which reflect the light leaked downwardly from the light guide plate substantially to the upward direction, and an optical sheet disposed on the light guide plate and the first to third frame members and which diffuses the light provided from the first frame member and the light guide plate and condenses the light substantially in the upward direction.