A light guide plate of a backlight unit is provided to remove a bright line around a light entrance surface by forming a prism protrusion in a direction in parallel to the light entrance surface of the light guide plate that employs a downward prism sheet. A light guide plate(10) includes one side surface serving as a light entrance surface(11a) and an upper surface serving as a light emitting surface(12). A prism pattern(13) including a ridge(13a) and a gully(13b) is formed on a bottom surface of the light guide plate from the light entrance surface to an opposite light entrance surface(11b) in order to uniformly emit a light entering from the light entrance surface to the upper surface of the light guide plate at a constant angle. A prism protrusion(14) is formed in the gully of the light entrance surface of the prism pattern such that it is in parallel to the light entrance surface and inclines toward the opposite light entrance surface in order to disperse the light concentrated to the light entrance surface.
