A backlight unit includes: a light source which generates light; a light guide plate which receives the light from the light source and guides the light to a display panel which displays an image with the light, the light guide plate including a light incident side surface to which the light from the light source is incident, and an opposing side surface which opposes said light incident side surface; and a reflection member disposed facing the opposing side surface of the light guide plate. Along a length of the opposing side surface of the light guide plate, the reflection member facing the opposing side surface includes at least two reflective portions having different reflectances from each other.