A rack can transmit a rotational torque in a webbing winding and tightening direction to a take-up spindle of a retractor via a pinion gear. In the event of a vehicular collision, this rack is pushed and driven by gas pressure. To rotate at an increased speed an outer clutch ring which can intermittently transmit a torque to the take-up spindle via a clutch mechanism, a speed-increasing gear unit is arranged between the pinion gear and the outer clutch ring.