Buckle retractor

The buckle tensioner has a tension transmission cable (12) acting upon a belt buckle, and a pressure accumulator compressible by a motor (48). The tension transmission cable is connected to the pressure accumulator by mechanical means, and the pressure accumulator is arranged so that an expansion of the accumulator effects a pulling away of the belt buckle for tightening of the seat belt strap. The pressure accumulator may include a helical spring (18) or a compressible fluid. A sensor (50) is provided to detect the end position of the pressure accumulator.