To raise a local outside heat transfer efficiency of a tube of a wake area and to obtain an enlarging effect of a heat transfer area by bending an end of each segment of a fin at its outer peripheral side in an axial direction of a fin tube via a folding line crossed with a line extended in a radial direction from an axis of the tube.

Fins 12 are provided on an outer periphery of a tube 11, and cutouts 13 of a radial direction of a depth Hc of the degree of 50% of a fin height H are provided from its outer periphery toward a center, and a plurality of segments 14 of substantially rectangular shape are radially formed. And, the end of each segment 14 at its outer peripheral side is formed with a bent piece 15 bent at a predetermined angle to a surface including the fin surface in an axial direction of the tube 11 along a bending line crossed with the line extended in a radial direction from the axis of the tube 11. And, outside fluid of the tube deflected in the flowing direction by the piece 15 is altered to a rear surface side of a tube 10 and detoured to a downstream side.