The present invention comprises a pulley, a shaft body which is rotatable relative to the pulley and is concentrically disposed radially inside of the pulley, a one-way clutch which is interposed at an annular space between the pulley and the shaft body, a rolling bearing which is disposed in the annular space adjacent to the one-way clutch in an axial direction, an inner annular seal which is provided outside the rolling bearing in the annular space, and an outer annular seal which is provided outside the inner annular seal and has a proximal end portion and a distal end side lip. The proximal end portion of the outer annular seal is fixed to one of an inner peripheral surface of the pulley and an outer peripheral surface of the shaft body, and the distal end side lip of the outer annular seal contacts the other peripheral surface.