PURPOSE: To obtain a heat exchanging unit with fins having a high heat exchanging rate and holding its characteristics for a long time by a method a slitted blank strip for the fins having a flange section with brazing material are wound on an outer circumferential surface of a metallic pipe, and heated and brazed.

CONSTITUTION: Tape-like brazing materials 6A having a width narrower than the blank strip, are stacked in the longitudinal direction of the blank strip 1 for fins and rolled and pressure-welded while slits 2 are formed in the lateral direction extending from (a) to (g). The surface on which the brazing material 6 is attached is directed downward, and the brazed section is bent, thus forming the flange 3. Fins 4 with the flange 3 are wound spirally on an outer circumferential surface of the metallic pipe 5 through the flange 3, heated at higher than the melting temperature of the brazing material 6, and brazed. Thus, the heat exchanging unit with the fins, having a high heat exchanging rate and unchanged characteristics even when subjecting to a heat cycle for a long time, can be obtained.