When a gas generating member of a pretensioner mechanism is activated in case of vehicle collision, a piston inside a pipe cylinder is moved from normal state and a pinion gear body is rotated. Thus, the teeth of the pinion gear portion come in contact with a push block and pushes it in outward direction in conjunction with a force of a block urging spring, whereby a rotating lever is rotated by the push block and the lower end portion of the rotating lever gets disengaged from the tip end portion of a gear-side arm. As a result, the gear-side arm is rotated by an urging spring in outer direction and rotates a mechanical arm through a coupling shaft to make the pawl engage a ratchet gear of a take-up drum unit.