Safety belt pretensioner

The seatbelt pretensioner (1) has a pyrotechnic actuator (2) with a piston (9) and a cord (3) whose one end (16) is connected to a fastening buckle of this seatbelt. The pyrotechnic actuator has a hollow body (5) including a pyrotechnic gas generator (6) and a sliding chamber (12) in which the piston slides, this chamber contiguous with the generator. The piston has a body (10) prolonged by a rod (11) of small diameter, with the body having a sealing joint (22). The pretensioner has a piston guide with lugs (18) placed on enlarged ends (14), with openings (17) in the casing wall (4).