A housing is rotatable synchronously with a crankshaft of an engine. A plurality of external teeth arrangements is respectively shaped into a ring form and is formed integrally with the housing in one piece and is configured to mesh with a plurality of chains, respectively, each of which is wound around the crankshaft or a sprocket that is rotatable. A cam plate is connected to a camshaft of the engine and is rotatable relative to the housing. A plurality of stoppers is formed integrally with the housing in one piece while the stoppers are configured to limit relative rotation between the housing and the cam plate within a predetermined range when the stoppers contact the cam plate. Each stopper is placed at a position, at which the stopper does not overlap with any of the external teeth arrangements in a view taken in an axial direction of the housing.