PURPOSE: To receive high rotational load by providing, on a boss, a rotational preventive projection having at least one rotational end face arranged substantially perpendicularly to a rotational direction of a cam shaft, and thereby receiving the rotational load by means of whole of the rotational end face.

CONSTITUTION: In a cam shaft 2 prepared by casting, cam pieces 6a, 6b and a boss 3 are arranged in line, and bearings 9, 10 are formed on both ends. A pair of rotation preventive projections 4 are formed on the boss 3 in a diameter direction, which projection 4 has a rotational end face 5 perpendicularly arranged to a rotational direction of a cam shaft. A cam gear 7 made of synthetic resin such as polyamtal resin is formed on an outer periphery of the boss 3 by injection molding. The rotational end face 5 perpendicular to the rotational direction of the cam shaft is formed on a plane passing an axial center of the cam shaft 2. Rotational load of the cam gear 7 is received by the rotational preventive projections 4 each having the rotational end face perpendicularly arranged to the cam shaft rotational direction. The rotational load is received by whole of the rotational end face, so that high rotational load can be received.