A heat transfer fin (3) comprises a plate-like base section (4), a cylindrical collar section (5), a recessed section (7) which has a sloped surface (7a), and a flare section (6) which, when combined with another heat transfer fin (3), is in surface contact with the sloped surface (7a) of the another heat transfer fin (3). The sloped surface (7a) of the recessed section (7) and the root of the collar section (5) are connected, the connection portion where the sloped surface (7a) of the recessed section (7) and the collar section (5) are connected is bent at an acute angle, and the root of the collar section (5) reaches a position beyond a reference plane (S) which is in contact with a surface (4a) of the base section (4), the surface (4a) being located on the side opposite the flare section (6).