A seat belt buckle (1) with a fastening fitting (2) for mounting in a motor vehicle has a retainer (5) permanently connected to the belt buckle (1) and a bolt (7) through which the retainer (5) is held rotatable with regard to the fastening fitting (2). A spring (6, 8) that impinges upon the belt buckle (1) in a rest position (R), has a supporting portion (65, 85), which restricts the rotational movement of the belt buckle (1) is restricted with regard to the fastening fitting (2).