To prevent cooling medium from flowing to the outside, and to prevent cooling medium transferred through a seam from flowing inside a heat exchanger pipe from an opening end of the heat exchanger pipe, even when the seam of a double-folded fin of the heat exchanger pipe is not efficiently soldered, or is not soldered at all.

An outer face of a raw pipe 1 possibly flowing fluid inside is continuously pressed in a pipe axial direction towards a center, and two walls are brought into close contact with each other in the pipe axial direction in the raw pipe 1, so as to form a two-folded fin. An inner pipe 20 is formed by the fin. The inner pipe 20 is inserted in an outer pipe 21, and a contact part of the outer pipe 21 and the inner pipe 20 is fixed by soldering, so as to obtain the heat exchanger pipe. The heat exchanger pipe 11 is built in the heat exchanger.