Provided is a valve timing controller capable of quickening a response in varying a relative rotational phase. When the valve timing controller is under a locking state, if an ECU outputs a phase maintenance signal indicative of a phase maintaining state wherein control for maintaining the relative rotational phase within a predetermined range by work fluid present in an advancing chamber and a retarding chamber is possible, an intermediate locking mechanism is switched to a lock-releasing state and also the relative rotational phase is maintained to an intermediate locking state.