PURPOSE: To provide an assembly type cam shaft which prevents vibration of a tightening bolt without providing a bolt hole in which a stress concentration tends to generate on the cam shaft.

CONSTITUTION: Hollow cam shaft pieces 2b provided in unit are coupled by Curvic Couplings, and a reversely tapered joint part 43 whose diameter increases gradually is provided at an end of a tightening bolt piece 40b in unit which is inserted in a hollow hole 12 of the cam shaft piece 2b. Moreover, a tapered sleeve 10 which has a tapered portion 14 which corresponds to the tapered joint part 43 at both inner ends and a plurality of split parts 11 along the longitudinal direction is fitted in the outside of the opposing tapered joint parts 43.