A low-voltage circuit breaker includes at least one fixed contact, for each pole, which is electrically connected to a terminal for connection to an electric circuit, and a corresponding moving contact which is associable/separable with respect to the fixed contact by a rotation of the moving contact. The low-voltage circuit breaker further includes an arc chamber positioned in correspondence of the fixed contact, and a rotating contact supporting shaft common to all poles, which is functionally connected to an actuation mechanism of the circuit breaker, where the actuation mechanism includes a kinematic system operatively connected to an actuation lever for opening/closing operations and provided with opening springs and a tripping shaft for releasing the kinematic system and allowing its movement from a closed to an open position. The low-voltage circuit breaker further includes, for each pole, a quick acting trip device.