In the event of a collision, the seat belt outer lap tensioner coordinates with the seat belt tensioner, instantaneously retracts the seat belt, and ensures the seat belt ability to restrain and protect the occupant at the chest and waist by firmly securing the occupant to the seat.

The structure of the seat belt outer lap tensioner is as shown in the figure.

When the seat belt outer lap tensioner operates, a piston within a cylinder moves by means of the gas pressure of a gas generator, a wire coupled to the piston is pulled, and an anchor is retracted. After retraction is complete, when the anchor and wire are pulled out by the forward movement of the occupant, a ball locks into the cylinder and locks the wire.