o obtain a method capable of manufacturing a curved part of a double tube type heat exchanger easily by a method wherein two sheets of boards provided with recessed parts of meandering configurations which are to be an outer tube later are put together and fixed so as to clamp a meandering inner tube and thus a meandering double tube is formed.

CONSTITUTION: Two sheets of guide boards 4, having recessed parts 6, 6′, a meandering recessed part 7 corresponding to an outer tube of a double tube and becoming later a cooling water passageway and a recessed parts 8, 8′ becoming later an inlet and an outlet of the cooling water, are put on together so as to pinch the inner tube 5 and the whole peripheries of both of the sheets are fixed together by welding or the like. In this case, a recessed part 9 is provided in one place at either a curved part or a straight line part of the recessed part 7 to regulate a position of the inner tube 5. According to such a method, the curved part of the outer tube may be formed easily and a meandering double tube type heat exchanger may be obtained as well.