Patent ID: 8720950

Claim:
A pretensioner comprising at least: a pipe; a plurality of force transmission members provided movably in the pipe to transmit a force for rotating a spool in a seatbelt retracting direction; a gas generator that generates gas in case of an emergency; a piston that is movably provided in the pipe and pushes the force transmission members when moved by a pressure of the gas; a ring gear at least rotatably provided and including a plurality of internal teeth on an inner periphery and a plurality of pressed portions on an outer periphery; and a pinion provided in a spool-side member to rotate the spool and including external teeth to be meshed with the internal teeth, wherein, in case of the emergency, the force transmission members press the pressed portions of the ring gear to rotate the spool in the seatbelt retracting direction, wherein all of the force transmission members are balls, and wherein the ring gear includes a stopper that stops rotation of the ring gear by contact with at least one of the force transmission members when the ring gear is rotated by a predetermined rotation amount by being pressed by the force transmission members.