PURPOSE: To improve the heat exchange efficiency of the titled heat exchanger by a method wherein in the double tube type heat exchanger used for a heat pump type cooling cycle, an inner tube is inserted into an outer tube after the inner tube is covered with a wire fin tube having a wire wound helically about the outer periphery thereof.

CONSTITUTION: The wire fin tube 8 is fusion-bonded to the outer periphery of the inner tube 7 made of steel by soldering or the like and the thick wire 9 is wound herically about the outer peripheral surface of the fin tube 8. Then the inner tube 9 is inserted into the outer tube 6 made of iron. In practice, water is flowed through the inner tube 7 and a coolant is flowed through the space between the inner tube 7 and the outer tube 6 in the direction reverse to the flow direction of the water in the inner tube 7 so that the coolant flows along the helical wire 9 as it is agitated. As a consequence, the coolant makes good contact with the inner tube 7 to thereby improve the heat exchange efficiency of the heat exchanger.