Construction is achieved that, together with preventing the occurrence of damage to a mandrel, is able to improve precision of the shape of a ring-shaped member after processing. A mandrel includes a pair of support shaft sections that are provided so as to be separated in the axial direction and so as to be concentric with each other, and a rolling shaft section that is concentrically provided in the axial direction between the pair of support shaft sections. One of the support shaft sections is provided in a state in which displacement in the axial direction with respect to the rolling shaft section is regulated. The other support shaft section is provided in a state in which displacement in a direction going away from the rolling shaft section is possible when a pressing force is applied in that direction.