PURPOSE: To improve the heat exchanging rate of the heat exchanger as well as the rigidity of fins and simplify the manufacturing work of the heat exchanger.

CONSTITUTION: Fins 21 are inserted into the inside of the U-shaped support member 24 of aluminum through openings 25 as shown by the arrow sign 21 in the diagram. In this case, the fins 21 are inserted and piled alternately one by one so that the protuberances 23, formed on respective fins 21, are abutted against each other at the tip ends 23' thereof, whereby, the intervals between fins are kept in constant substantially. After all of the fins 21 are piled, refrigerant pipes 18, having outer diameters slightly smaller than the diameters of through ports 22, are penetrated through the through ports 22. Next, metallic piping members 18', whose diameter is larger than the inner diameter of the refrigerant pipes 18, are fitted to the refrigerant pipes 18 to engage respective refrigerant pipes 18 with the fns 21. Cool air flowing through the heat exchanger, is disturbed not only by the refrigerant pipes 18 but also by the protuberances 23 and the surface area of the fins 21 is increased by the protuberances 23, therefore, heat exchanging area between the cool air and the fins 21 may be increased.