A parallel guide portion as an integral structure of a sprocket and a vane, as well as a slant guide portion, are arranged alternately on the same circumference, with circumferential gaps being formed between said guide portion and the parallel guide portion, said guide portion having a shape such that the circumferential gaps become smaller in one axial direction of a cam shaft. Wedge members are disposed in the circumferential gaps respectively and are moved in one axial direction to fill up the circumferential gaps, thereby fixing the phase between the sprocket and the vane into a locked state. The wedge angle of each wedge member is set sufficiently small and, by utilizing varying torques acting on the cam shaft, said members are each moved and locked in one axial direction with a spring. Said members are actuated in an opposite axial direction with oil pressure to release the locked state, thereby permitting a phase angle control. By utilizing a varying torque acting on the cam shaft, the phase of the cam shaft is returned for itself to an intermediate position and is locked without looseness.