A discharge lamp lighting apparatus includes a transformer unit, a casing for housing the transformer unit, and a circuit board including circuit components. In the casing, the circuit board is joined to the casing and the transformer unit is fixed to the circuit board through a heat conductive member having thermal conductivity of more than 0.1 W/(mk). Heat produced by the transformer unit is transferred to the casing through the heat conductive member and released through the casing effectively. In the lighting apparatus, therefore, while the transformer unit is arranged relatively close to the circuit components, the heat can be prevented from affecting the circuit components.