To provide a shaft body manufacturing method capable of simply and inexpensively manufacturing an integrated cam shaft or the like which is manufactured by cutting.

The cam shaft 1 comprises a shaft part 2 and first to fourth cam parts 3-6, and the cam parts 3, 5 and 6 comprise first and second longitudinally split pieces 31, 32, 51, 52, 61 and 62. The shaft part 2, each split piece and the second cam part are respectively manufactured, assembled, and fitted between conductive electrodes 73 and 76 of a conductive joining machine 70 of a conductive joining equipment 7, and the DC current or the pulse current is allowed to run under the predetermined pressure for the predetermined time, and left for the predetermined time in a predetermined heated condition in a heat treatment machine 80. As a result, the cam shaft with each joining surface joined with the joining strength equivalent to the strength of the base material is provided.