A variable valve timing adjusting mechanism includes one-way valves in a hydraulic supply passage in an advance hydraulic chamber and in a retard hydraulic chamber respectively and a drain oil passage bypassing each of the one-way valves disposed in parallel in the hydraulic supply passage of each hydraulic chamber. Drain switching valves are disposed in the respective drain oil passages. A controller opens the drain switching valve in a side of the hydraulic chamber where oil is discharged when a deviation between a target displacement angle and an actual displacement angle is more than a predetermined value to perform the maximum speed control for driving the adjusting mechanism in a direction of the target displacement angle at the maximum speed. The controller closes the drain switching valve in a side of the hydraulic chamber where oil is discharged when the deviation between the target displacement angle and the actual displacement angle is small to perform the holding control for stopping/slowing the variable operation of the adjusting mechanism.