PURPOSE: A backlight unit is provided to effectively cool heat of a light emitting diode, thereby guaranteeing lifetime of the light emitting diode. CONSTITUTION: Respective diffusing plates(31,33) diffuse heat of a light emitting diode to a front side. A heat absorbing unit(71) of a heat pipe(70) is installed in a longitudinal direction of the diffusing plate. Heat of the light emitting diode is uniformly diffused in the longitudinal direction of the diffusing plate by the heat absorbing unit. A temperature is uniformly maintained between the light emitting diodes. A heat sink is cooled by natural convection current. Or the heat sink is cooled if a fan(90) of a lower panel generates a heat absorbing unit.
