A rotor includes a cylindrical portion, a front wall, and first and second rotor arms. The front wall is formed on an inner periphery of the cylindrical portion near its front end. The first and second rotor arms are arranged opposite one another on the sides of the cylindrical portion. The front wall includes a link portion and a disk portion. The outer periphery of the cylindrical portion where the link portion is linked is overlaid by the spool when the spool is at a foremost position. The disk portion is integrally linked to the link portion. The link portion includes an annular portion and a tapered portion. The annular portion is linked to the inner periphery of the cylindrical portion at its front end. The tapered portion is linked to the inner periphery of the annular portion and is tapered so that its diameter rearwardly decreases.