A pretensioner includes a drive wheel provided with a plurality of engaging teeth for rotating a spool, the spool for winding up a webbing for fastening a passenger; and an elongated resin component that transmits power to the drive wheel during an emergency, wherein the plurality of teeth is positioned such that, when one engaging tooth is caused to contact a tip of the elongated resin component in an approximately planer manner, another engaging tooth adjacent to the one engaging tooth in a direction opposite to a rotation direction can contact a side surface of the elongated resin component.