An energy dissipator for a vehicle safety belt includes a reel on which one end of the belt is wound and anchored, the reel having two internal screw threads of opposite pitch in which respective bushes are threaded, so that in the event of an unwinding force on the reel due to a tension in the belt, for example on impact, the bushes are screwed towards each other and squash a deformable element interposed between the bushes.