A Circuit breaker comprising: a case (1); terminals (2,3) for connection to an electric circuit; separable contact means (4,5); an actuating knob (6) which rotates about a first pivot (7) that is rigidly coupled to the case (1) between a closed position, in which the contacts are coupled, and an open position, in which they are separated, a first spring (8) being associated with the knob (6); electric arc quenching means; protection means against electrical faults; a kinematic mechanism, which comprises a first supporting lever, on which the moving contact (5) is arranged, the supporting lever being operatively connected to the knob by virtue of a connecting element (18), and a second release lever, which is operatively associated with the protection means, the first and second levers being mounted coaxially and rotating about a second pivot (19) that is rigidly coupled to the cases, a second spring being associated with the first and second levers; the kinematic mechanism further comprises a third actuation lever (24) which is operatively coupled to the moving contact (5), a third actuation spring (25) being associated with the third actuation lever (24) and applying to it a force that is suitable to facilitate an adequate coupling pressure between the contacts (4,5) in the closed position and to cause the rotation thereof together with the moving contact (5) when the protection means intervene.