To realize size and weight reductions of a cam shaft while forming its shape so as to increase a connection force between a shaft portion and a cam piece.

This cam shaft is provided with the shaft portion in a cylindrical form and the cam piece having a shaft hole for engaging with the shaft portion, and the shaft portion is connected with the cam piece by expanding the shaft portion by bulging as the shaft portion is inserted into the shaft hole of the cam piece. The cam piece includes a center reference portion in the axial center of the shaft hole, and a recessed end portion provided circumferentially along an opening in a recessed form in the inner periphery side near axial end parts. A periphery recess which recesses peripherally is formed on the inner periphery of the center reference portion, and a plurality of diameter recesses which recess in a circumferential direction are formed on the inner periphery of the recessed end portion with intervals along the circumferential direction. The shaft portion forms bulged portions which are expanded and deformed to be protruded to the periphery recess and the diameter recesses on the cam piece by bulging.