A variable valve timing system is provided with a relative rotation controlling mechanism allowing relative rotation of the housing member and the rotor member by an unlock operation through the supply of operation fluid, and restricting the relative rotation of the housing member and the rotor member at an intermediate angle phase between a most retarded angle phase and a most advanced angle phase by a lock operation through the discharge of the operation fluid. A hydraulic pressure circuit controls the supply and discharge of the operation fluid to the relative rotation controlling mechanism and also controls the supply and discharge of the operation fluid to the advanced angle chamber and the retarded angle chamber. The hydraulic pressure circuit is adapted to discharge the operation fluid from the advanced angle chamber, the retarded angle chamber and the relative rotation controlling mechanism when the combustion engine is started.