Each of vibration dampers is separated from each circumferentially adjacent one of the vibration dampers upon cutting of each of a plurality of connectors, which is initially integrally formed with the vibration dampers to circumferentially join between corresponding circumferentially adjacent two of the vibration dampers to form a single closed loop body. At least a part of each of first and second circumferential end portions of each vibration damper is engaged with a corresponding one of outer protrusions of a centerpiece in a circumferential direction of a stator. A primary recess is radially inwardly recessed at an outer peripheral portion of the vibration damper and is engaged with a corresponding one of primary protrusions of the stator in the circumferential direction of the stator.