The present invention provides a winder used for a force limiting safety belt, comprising: a winder frame, a reel and a torsion bar. wherein, the winder frame comprises two opposite sidewalls, the corresponding positions of the two sidewalls having circular openings provided, the circular openings having internal toothed segments; the reel comprising a spindle through hole provided along the central axis of the spindle, two detachable end covers provided respectively on the two ends of the spindle, the end covers having external teeth provided along the periphery of the end covers; the torsion bar is divided into two segments in axial direction which are connected to each other by adjoining ends; in a free state, the reel is able to rotate and float provided within the winder frame, two end covers being provided in the circular through opening on the two sidewalls of the winder frame.