Radiator caps (266) and radiator tubes (211) are heat brazed with an ingot Z of a sacrificial material being disposed in the interior of a radiator tank main body (234), whereby, as the ingot Z of the sacrificial material is heated while being surrounded by the radiator tank main body (234), the evaporated sacrificial material is allowed to adhere to internal surfaces of the radiator tank main body (234) relatively uniformly, the sacrificial material so adhering to the internal surfaces being then allowed to be radiated into aluminum constituting the radiator tank main body (234) to thereby form an alloy layer (a corrosion preventing layer) containing therein the sacrificial material heavily on the internal surface of the radiator tank main body (234).