The belt tensioner includes a tensioning device which rotates the spool (18) in the coiling-up direction of the belt (20) if a deceleration of the vehicle exceeds a prescribed value. An energy absorbing device is connected to the spool and set in motion with it and deformed by it to prevent an increase in belt tension if a rotational force acts in the unwinding direction of the belt. A restoring device acts through the rotational force in the unwinding direction of the belt by means of the energy absorbing element.
