To suppress the burring of a corrugated fin and to prolong the service life of a forming cutter by providing clearance at engaging cutting edges in a pair of corrugated fin forming cutters engaged with each other.

A prescribed clearance L is provided between a cutting edge part 8 of one corrugated fin forming cutter 3 (made of high speed steel or sintered hard alloy) and a cutting edge part 8 of another corrugated fin forming cutter 3 (made of high speed steel or sintered hard alloy) in order not to rub each other at engaging. The clearance L is set in the range of 0-40μm. By this method, corresponding cutters are not rubbed with each other, the burring of corrugated fin is prevented, the service life of the corrugated fine forming cutter is prolonged.