PURPOSE: To facilitate formation of a header with an insertion hole by a method wherein a header has a cylinder body formed by bending a flat material having an insertion hold for a tube or by combing a flat material having an insertion hole for a tube and other plate.

CONSTITUTION: Heat exchange is carried out between the flowing fluids on the inside and outside of tubes 2 provided with a plurality of interior fluid passages. A header 4 is a cylindrical tank connected to both ends of each tube 2, and it is provided to distribute and guide a supplied fluid to each tube 2 or collect the fluid passing through each tube 2. A cylinder body 5 is formed such that a flat plate 8 made of the same material as that of the tube 2 is bent in the shape of a cylinder and a cover 9 is attached over the seam 8a by brazing. This constitution facilitates formation of the header 4 having an insertion hole 11.