Circuit breaker with a locking device for a tilting lever provided for switching the circuit breaker on and off, wherein - a switch housing enclosing the circuit breaker comprises an opening for the tilting lever, - an actuator mechanism operatively connected to the main contacts of the circuit breaker comprises a shifting gate to which the tilting lever protruding from the switch housing is rigidly connected, the shifting gate being rotatable about an axle which is fixedly mounted opposite the switch housing, - the tilting lever has at least two stable positions, and more specifically positions at least corresponding to the on-position and the off-position of the main contacts, wherein the tilting lever is in an intermediate-position different from the off-position, when the main contacts are welded, and - the locking device which may be mounted on the switch housing comprises a cover which may enclose the tilting lever in the off-position, the cover comprising at least one locking through hole opening for holding a shackle lock and being fastenable on the switch housing. characterized in that - the shifting gate comprises near the tilting lever a threaded hole which is approximately radial in relation to the axle and which can be accessed from the exterior through the switch housing when the tilting lever is in the off-position, - the locking device comprises near the cover a through hole, through which a threaded shank of a cap screw extends to the shifting gate, the cap screw being provided for fastening the locking device on the switch housing, - the angle between the threaded hole and the tilting lever on the one hand, and, when the locking device is mounted, the distance between the through hole and a first inner wall of the cover that is closely opposite the tilting lever in the off-position, on the other hand, are such that only when in the off-position, the tilting lever is enclosed by the cover, and simultaneously the through hole and the threaded hole are aligned, and - the cap screw tightened in the threaded hole may be covered by a shackle of the shackle lock that has been inserted in the locking opening. - a switch housing enclosing the circuit breaker comprises an opening for the tilting lever, - an actuator mechanism operatively connected to the main contacts of the circuit breaker comprises a shifting gate to which the tilting lever protruding from the switch housing is rigidly connected, the shifting gate being rotatable about an axle which is fixedly mounted opposite the switch housing, - the tilting lever has at least two stable positions, and more specifically positions at least corresponding to the on-position and the off-position of the main contacts, wherein the tilting lever is in an intermediate-position different from the off-position, when the main contacts are welded, and - the locking device which may be mounted on the switch housing comprises a cover which may enclose the tilting lever in the off-position, the cover comprising at least one locking through hole opening for holding a shackle lock and being fastenable on the switch housing. - the shifting gate comprises near the tilting lever a threaded hole which is approximately radial in relation to the axle and which can be accessed from the exterior through the switch housing when the tilting lever is in the off-position, - the locking device comprises near the cover a through hole, through which a threaded shank of a cap screw extends to the shifting gate, the cap screw being provided for fastening the locking device on the switch housing, - the angle between the threaded hole and the tilting lever on the one hand, and, when the locking device is mounted, the distance between the through hole and a first inner wall of the cover that is closely opposite the tilting lever in the off-position, on the other hand, are such that only when in the off-position, the tilting lever is enclosed by the cover, and simultaneously the through hole and the threaded hole are aligned, and - the cap screw tightened in the threaded hole may be covered by a shackle of the shackle lock that has been inserted in the locking opening.