PURPOSE: To obtain the heat exchanger which has a small heat conduction resistance and is compact in size and which is manufactured at low cost, by a method wherein a flow regulating member for a heat medium is arranged within an inner cylinder having a number of fins on the inner surface thereof leaving a clearance from the latter so that the clearance serves as a primary side fluid passage and a heat conductive member having a secondary side fluid conduit embedded therein is bonded tightly to the outer circumference of the inner cylinder.

CONSTITUTION: The heat medium which is a high temperature gas from a primary side fluid inlet port 5 enters a primary side fluid passage 10 divided into a number of sections, through an inlet chamber 11. In this case, the heat medium radiates heat to the water in a pipe 13 through the inner surface of the inner cylinder, fins 2 and a heat conductive member 16, condenses to become a low temperature liquid which collects in an outlet chamber 12 and flows out from a primary side fluid outlet port 6. At the same time, the water enters the pipe 13 from a secondary side fluid inlet port 14, flows upward along the outer periphery of the inner cylinder in a helical fashion so as to be heated to an elevated temperature by the high temperature heat medium and flows out from a secondary side fluid flow-out port 15 provided at the upper part of the heat exchanger. Thus, as the heat medium flows vertically from the upper part down to the lower part of the heat exchanger, the condensed and liquefied heat medium falls down smoothly to the lower part of the heat exchanger. Accordingly, the liquid film generating on the heat transfer wall of the heat exchanger at the time of condensation of the heat medium become thin so that the increase of thermal resistance due to an increase in the thickness of the liquid film is prevented and the heat transfer efficiency of the heat exchanger is improved.