Where power components are fixed on a heat sink 1 inclusive of a heat sink base 1b and cooling fins 1a provided on the heat sink base 1b, one 1c of the cooling fins, which is made thicker, is arranged upright on the heat sink base 1b. And a high heat-generating power component 3 is fixed to the heat sink base 1b and middle heat-generating power components 5, 6 are fixed to the cooling fin 1c.