Abstract: A lock member includes a closed cylindrical portion having lock teeth and a fixation boss provided inside the cylindrical portion and inserted in a fitting hole formed at one end of the take-up drum and facing the take-up drum along an axial direction of the cylindrical portion. A stopper mechanism includes a ring member whose inner peripheral surface is mounted on the fixation boss and whose outer peripheral surface is fitted in the fitting hole so as to prohibit relative rotation with respect to the fitting hole. The ring member is movable relative to the fixation boss in the axial direction of the take-up drum by the relative rotation with respect to the fixation boss. Further, movable area allowed for the ring member to move on the fixation boss axially outward with respect to the take-up drum has an movable end located inside of the closed cylindrical portion.