PURPOSE: To shorten a span of washing time in making each other side of both first and second heat exchangers directly washable as well as to prevent any drop in cooling efficiency from occurring.

CONSTITUTION: A frame body 25 is interposed between a radiator 22 and an oil cooler 23 and thereby a washing space S is formed there, while this frame body 25 consists of a pair of connecting frame parts 26 and 26 connecting the radiator 22 and the oil cooler 23 and a pair of lid frame parts 27 and 27 detachably attached to both end sides of each connecting frame part 26. Accordingly, dust stuck to respective radiating fins 22B and 23B or the like of the radiator 22 and the oil cooler 23 is directly removed by dint of steam sprayed out of an injection nozzle of a steam washing machine inserted into the washing space S in a state that the paired lid frame parts 27 are taken away.