[OBJECT] After having determined a phase angle, the phase angle is maintained as the determined one without consuming electric power. [ACHIEVING MEANS] An intermediate member 14 is movably disposed on the outer periphery of an inner cylinder part 12 that is relatively rotatably disposed with respect to an outer cylinder part 10 to which a driving force of a crankshaft is transmitted and that is connected to a camshaft. In a process in which the intermediate member 14 moves in the axial direction when a solenoid 74 or a solenoid 76 is energized, balls 46 and 48 move in mutually opposite directions in response to a displacement in the axial direction caused by the movement of the intermediate member 14, and the phase between the outer cylinder part 10 and the camshaft 2 is variably adjusted. After the intermediate member 14 is set at an advance position or a retard position when the solenoids 74 and 76 are deenergized, the balls 46 and 48 stop moving for the input of torque from the outer cylinder part 10 or from the camshaft 2, anda self-locking state is reached.