PROBLEM TO BE SOLVED: To enable an enhancement in circularity of the thickened part of a metal shaft member when the thickened part is to be formed by using the axis thickening molding method.SOLUTION: An axis thickening molder 1, which thickens the periphery of the action part of a work-piece W in the radial direction of a central axis X1 to form a thickened part Wa having a larger diameter than the work-piece W, includes an outer diameter measuring apparatus 30 that measures the outer diameter of the thickened part Wa for every phase angle around the central axis X1 and a control apparatus 20 that controls rotational speed N, compression stress σa, and flexural stress σb. The control apparatus 20 has such a configuration as to adjust at least one of the rotational speed N, compression stress σa, and flexural stress σb so that the thickening amount at a predetermined phase angle in a radial direction when the outer diameter at a predetermined phase angle in the outer diameter of the thickened part Wa mea
