In an acceleration sensor, a guide portion is formed on a swing push-us member contiguous to a pushing portion and further to a pull-out direction side than the pushing portion. A top-edge portion of the guide portion is sloped to gradually get lower on progression away from the pushing portion in the pull-out direction. When a coupling claw moves in the take-up direction together with the sensor gear, the guide portion contacts the coupling claw from below the leading end of the coupling claw. The guide portion swings the coupling claw upwards as the sensor gear is rotating in the take-up direction, and guides the coupling claw to be on the pushing portion. The swing push-us member can be prevented from unintentionally obstructing the coupling claw when the sensor gear is returning to the initial position, even without provision of structure to restrict the swing push-us member from rising.