Abstract: A VVT mechanism is comprised of an internal rotor 29 connected to a cam shaft 12 and a housing 28 connected to an output shaft of an engine, and is further provided with a lock mechanism 43, 49 for restricting the relative rotation of the internal rotor 29 and the housing 28. An electronic control unit (ECU) 17 controls the driving of the VVT mechanism 11, and when changing over the direction of the relative rotation at a specific relative angle of rotation for actuating the lock mechanism 43, 49, after executing holding control for supplying a predetermined amount of oil to the advanced-angle side and delayed-angle side hydraulic chambers for a predetermined time duration, the ECU 17 effects a changeover to advanced-angle control. During the changeover, oil pressure necessary for canceling the lock mechanism is constantly supplied, so that it is possible to prevent unprepared actuation of the lock mechanism.