When a pinion gear body (33) rotates co-axially with rotational axis of the take-up drum (6), a first rotation body (76) which is fixed to the pinion gear body co-axially rotates relatively to a second rotation body (77) which is mounted to the pinion gear body co-axially, as well, and does not rotate during initial rotation of the pinion gear body. Thereby, an engagement member (29) which is rotatably supported by the first rotation body and fitted to the first and second rotation bodies protrudes radially and outwardly. The engagement member that has thus projected gets engaged with the take-up drum. In this stage, the engagement member is pressed and moved by a guiding portion of the second rotation body in response to the relative rotation so as to be guided in an outward radial direction.