Belt retractor

The invention relates to a belt retractor (10) for a seat belt, with a belt reel (20) for winding up and unwinding the seat belt, and a torsion bar (30) which is arranged outside the belt reel (20) and is connected at one bar end (32) to a switchable fixing device (50), the switchable fixing device (50), in one state, keeping the bar end (32) rotationally fixed and, in another state, permitting rotation of the bar end (32). According to the invention, it is provided that the switchable fixing device (50) has a displaceable piston (80) which, with a piston portion, in a locking position, can secure the bar end (32) against rotation and, in a release position displaced in relation to the locking position, releases the bar end (32).