PURPOSE: To absorb the variance in dimensional accuracy and to make said accuracy uniform by setting the contact angle of ≥3 pieces of pressing rollers which contact with the fillet part of a crank shaft at ≥2 kinds different from each other so that the residual stress region is extended over a wide range.

CONSTITUTION: ≥3 Pieces of pressing rollers 3 are pressed to the outside circumference in the fillet part 2 of a crank shaft 1. The rollers 3 are pressed to said fillet part 2 with at least two kinds of contact angles. Residual stress areas A1, A2 extending to the angles different from each other are generated in the fillet part 2 and the reinforcing regions are expanded over a wide range as a whole. The variance in the accuracy of the two sizes is thus absorbed and the accuracy is made uniform over the entire part.