It is the main object of this invention to provide a circuit breaker in which the movable contacts have sufficient opening force and opening distance, and in which the breaking time is short. In order to attain the object, the circuit breaker of this invention is provided with a dead center link mechanism comprising a movable contact link which is rotatably supported by the arms of a cross bar which is operated so as to be capable of opening-closing the circuit and tripping by means of a trip-free mechanism, and a toggle spring which is bridged between the cross bar and the movable contact link. When a large current such as a short-circuit current flows, a movable steel plate attracted by an electromagnet for instantaneously tripping hits a rod for supporting the movable contacts which is connected to the movable contact link, whereby the dead center link mechanism makes the movable contacts open at high speed from the fixed contacts. As a result of such an operation, the current-limiting effect in this circuit breaker is excellent and breaking performance is improved.