To provide a backlight unit for use in a liquid crystal display device and so on, which is capable of overcoming a problem of interference due to expansion and contraction of a light guide plate and an optical sheet and preventing a strange noise by clicking, a backlight unit includes a support plate, a light guide plate that is disposed in the front side of the support plate and emits light, which is introduced from a light source through the end side of the light guide plate, through the front side of the light guide plate, an optical sheet that is disposed in the front side of the light guide plate, and a liquid crystal panel maintenance member that is disposed in the front side of the optical sheet, wherein the light guide plate and the liquid crystal panel maintenance member hold and fix the optical sheet at one point.