In a discharge lamp unit, a casing member arranged such that the casing member holds a circuit board therein and holds a discharge lamp supporting section being exposed outside of the casing member. A thermal absorption protect layer is formed on the surface on the side on which the discharge lamp supporting section is exposed. The thermal absorption protect layer allows the casing member to inhibit absorption of radiant heat induced by the discharge lamp. Since the thermal absorption protect layer inhibits the casing member from absorbing the radiant heat from the discharge lamp, the amount of heat generated by the discharge lamp reaching the circuit board may be reduced. Therefore, the circuit board is not easily heated.