The present invention relates to a tensioning device for a seat belt device, with a gas generator (10) for generating a pressurized gas, a piston (2) that can be driven by the pressurized gas, a tension cable (5) connected to the piston (2), which tension cable can be connected to a safety belt component that is to be set into a tensioning movement and which tension cable extends through the piston (2), a guide part (3) arranged on the tension cable (2), and a tensioning tube (6) for receiving the piston (2) and the guide part (3), which is characterized in that the guide part (3) is arranged on the side of the piston (2) facing away from the gas generator (10) and is movable relative to the piston (2).

There is provided an actuator curved inner length measurement apparatus for a fluid pressure actuator that includes a tubular actuator main body portion having a tube circumference of which one side is shortened and curved due to increase in internal pressure in a tube and that has a proximal end side along a tube axis which is fixed to a base body and has a distal end which moves relative to the base body, the actuator curved inner length measurement apparatus including: a wire member having one end side attached to the base body and a middle portion disposed on a curved side of the actuator main body portion 22 to conform to curved deformation; a wire holding member that holds the wire member at a position along the actuator main body portion; and a measurement unit that applies tension to the wire member and measures a length change amount of the wire member.

A rotary actuator includes: an output shaft; a housing in which a cylinder is defined, the cylinder having a circular arc shape around the output shaft; a piston adapted to move inside the cylinder by action of a pressure medium; and an arm connecting the piston and the output shaft. When viewed in plan from a direction parallel to the output shaft, a top surface of the piston has three equally divided regions divided in the radial direction from the center of the output shaft, the middle one of the three regions is a central region. When viewed in plan from the direction parallel to the output shaft, a connection point between the piston and the arm is situated on a virtual line that is orthogonal to the top surface and passes through the central region.