An object of the present invention is to provide a heat exchanging fin capable of preventing cracks from forming in the flares of the collared tube holes, even if the metallic plate section is made of the thin and tough material. In the heat exchanging fin, a metallic plate section has a plurality of tube holes. A plurality of collars are respectively extended from edges of the tube holes. A plurality of flares are respectively formed at front ends of the collars. Each flare includes a plurality of radially extended sections, which are radially outwardly extended from the front end of each collar, and separation between the metallic plate section and each radially extended section is fixed.