To provide a heat exchanger, a tube for the heat exchanger, and methods of manufacturing them, capable of easily continuously molding tubes, and preventing defective brazing between the tube and a tank portion.

A caulked portion 111 of the tube 11 is configurated in such manner that edge portions 112, 113 of strip-shaped members are formed in a state of being overlapped in a width narrower than a minor axial direction Y of a flat cross-sectional shape of the tube. Thus the tube continuous body can be transported while surely caulking the caulked portion 111 from both sides. Further an outer peripheral face 111a of the caulked portion 111 can be smoothed in caulking work, and a tube insertion port 32a can be surely brazed even when it has the simple shape.