PURPOSE: To improve strength by forming the residual stress distributing over a wide range in the fillet parts on the work side by tilting a pressurizing roll with the eccentricity and inclination in the fillet parts of a backup roll.

CONSTITUTION: A freely rotatably backup roll 2 having fillet parts 4 that possess the circumferential surface corresponding to the fillet parts Wa of the work W is provided to a pressurizing device with a pressurizing roll for the fillet parts and the fillet parts Wa of the work W are pressed to the parts 4. The circumferential surface forming the parts 4 of the roll 2 is formed as a circular circumferential surface having the center deviated from the axial center A of the roll 2, and the fillet parts 4 are so formed on the circumferential surface that the cross section C running the fillet part is inclined to the axial line of the roll 2.