The spool shaft comprises a shaft portion, two annular first annular portions arranged on opposite ends of the shaft portion, and an annular second larger diameter portion arranged on the end of the shaft portion positioned remote from a center of the spool. Each of the first annular portions and the second larger diameter portion have an outer diameter that is larger than the outer diameter of the shaft portion. The second larger diameter portion is arranged on an outward side of the first annular portion in the axial direction so as to create a space therein between the first annular portion and second larger diameter portion.