PURPOSE: To improve the pressure tightness capability of a heat exchanger tube to make the application of a high pressure fluid possible by a method wherein an indirect member with a favorable heat conduction is inserted in a gap between heat exchanger tubes, and a heat exchanging reaction is performed through the indirect member.

CONSTITUTION: A heat-exchanger 101 being equipped with a heat exchanger tube 1 in which a high temperature fluid flows and a heat exchanger tube 2 in which a low temperature fluid flows is constituted in such a manner that the heat exchanger tubes 1, 2 are arranged so that the flowing directions of the fluids may become in parallel, and an indirect member 3 made of a material with a favorable heat conduction, of which the processing is easy, is inserted in a gap between the heat exchanger tubes 1, 2, and the heat exchanger tubes are fixed by a fixing member 4. By this method, the pressure tightness capability of the heat exchanger tubes at the time of manufacture is ensured, and the range of fluids to be applied can be expanded.