A heat exchanger includes a pair of end plates closing opposite ends of a cylindrical core case, and a plurality of heat exchange tubes each supported at opposite end portions by the end plates. The end plates have support holes, and opposite ends of the tubes are inserted into corresponding support holes in the end plates. Each of the tubes is formed by bending a plate material so that opposite side edge portions of the bent plate material are superimposed on each other, one of the superimposed side edge portions, located inward of the other of the superimposed side edge portions, forming an inner plate portion, the other of the superimposed side edge portions forming an outer plate portion, and then welding a weld bead through the thickness of one of the inner and outer plate portions to fuse to the other plate portion.