A driven-side rotator is rotatable synchronously with a camshaft and is supported between a gear member and a sprocket member of the driving-side rotator in an axial direction. A stopper portion of the driven-side rotator is adapted to contact the driving-side rotator in a rotational direction to limit a change in a relative phase between the crankshaft and the camshaft. The stopper portion radially outwardly projects from a small diameter portion provided at one end part of the driven-side rotator. A large diameter portion is provided at the other end part of the driven-side rotator and has a radial size that is measured from a rotational axis to a radially outer peripheral surface of the large diameter portion and is equal to or larger than that of the stopper portion.