PURPOSE: To prevent a crack of a cam frame, etc., by forming a hardened layer on a cam frame surface layer part, also fitting it into a hollow shaft, and subsequently, expanding a diameter of the hollow shaft, and thereafter, grinding the outside periphery of a cam frame and finishing it.

CONSTITUTION: A cam frame 3 is formed by forging a steel material, and thereafter, a hardened layer 31 of a roughly uniform depth is formed by hardening on the whole periphery of a surface layer part. Subsequently, the cam frame 3 and a journal 6 are inserted into a prescribed position of a hollow shaft 2, and closed in upper and lower metallic dies 20, 21. In this state, an emulsion liquid, etc. are injected into the hollow shaft 2, and also the emulsion liquid is compressed and pressed. In this case, the hollow shaft 2 contracts as to its overall length and also expands to the outside, the inside peripheral surface of the cam frame 3, the journal frame 6, etc. are brought to a plastic deformation, and a deformation of a cam pfofile is prevented. Subsequently, a cam frame outside periphery 34, etc. are ground and finished, and a cam shaft 1 is obtained. In this way a crack of the cam frame 3 is prevented, and also its finish margein can also be reduced.