the ends on the shorter sides of the brazing material sheet become abutted against the staged portions 30 and thus the brazing material sheet 29 becomes attached to the tube insertion hole formation surface 20 a at each of the tanks 2 and 3 in addition claw tabs 32 are disposed at the caps 21 in the example so that the brazing material sheets 29 can be attached onto the tube insertion hole formation surfaces 20 a even more firmly by holding the edges of the brazing material sheets 29 along their shorter sides with the claw tabs 32 when the caps 21 are mounted at the openings of the tanks 2 and 3 when the heat exchanger 1 having been temporarily preassembled undergoes the process of furnace brazing the tanks 2 and 3 and the heat exchange tubes 4 are brazed together via the brazing material 28 supplied to the tube insertion hole formation surfaces 20 a at the tanks 2 and 3 also as indicated by the dotted lines in fig7 the brazing material 28 is supplied to the bonding regions 4 d at the heat exchange tubes 4 through capillary action to penetrate the spaces between the joining surfaces of the bonding regions 4 d along the longer sides of the heat exchange tubes 4 thereby brazing the bonding regions 4 d as well thus even though the heat exchange tubes 4 are formed through roll forming it is not necessary to cover the surface of the sheet material with a brazing material layer which allows the.