A self-locking belt retractor with a belt shaft which is mounted rotatably in a frame having a belt-sensitive a blocking device. A disc cam (1) mounted rotatably on the belt shaft, is pretensioned by a spring in the extension direction of the seat belt and on which an inertial mass (5) is mounted pivotably about a pivot axis (S). A projection (11) limits relative movement between the inertial mass (5) and the disc cam (1) is provided on the inertial mass (5) and/or on the disc cam (1).