A variable valve timing mechanism changes a relative rotation phase of a camshaft to a target phase based on hydraulic pressure supplied to an advance and a retard sides pressure chambers. A lock mechanism is placed in a locked state in which the relative rotation phase is locked at a maximum retard phase when the hydraulic pressure in the advance and the retard side pressure chambers is low, and that is placed in an unlocked state in which the locked state is released when the hydraulic pressure becomes high. Hydraulic pressure regulations in a first mode that changes the relative rotation phase to a side toward the maximum retard phase and in a second mode that changes the relative rotation phase to a side away from the maximum retard phase are executed in combination during a period from when an operating switch is turned off until a crankshaft stops rotating.