When an intermediate lock by an intermediate lock mechanism is released, one of two lock keys, which restricts a shift in a direction opposite to a direction that valve timing of an intake valve has been controlled by controlling the valve timing of the intake valve to a phase-advance side with respect to an intermediate lock position, is pulled out of an engaging recessed portion. Thereafter, the other of the two lock keys is pulled out of an engaging recessed portion by controlling the valve timing of the intake valve to a phase-retard side with respect to the intermediate lock position. Therefore, the intermediate lock by the intermediate lock mechanism can be released, while avoiding the lock keys from being pushed against the respective engaging recessed portions.