A circuit breaker having a switching mechanism having an 'OFF' position for manually breaking a circuit, an 'ON' position for manually closing the circuit, and a TRIP' position for automatically breaking the circuit, the circuit breaker comprising: an over current relay configured to generate and output a first trip control signal when an abnormal current on the circuit has been detected, and to generate and output a second trip control signal when a voltage applied to the circuit has been detected as a voltage less than a predetermined reference voltage; a magnetic trip mechanism electrically connected to the over current relay, and configured to provide a first mechanical driving force when receiving the first trip control signal from the over current relay; a low voltage trip mechanism electrically connected to the over current relay, and configured to provide a second mechanical driving force when receiving the second trip control signal from the over current relay; a first micro switch configured to generate and output a first trip indicating signal indicating that the circuit breaker has performed a trip operation due to the occurrence of an abnormal current on the circuit, by converting the first mechanical driving force received from the magnetic trip mechanism into an electric signal; a second micro switch configured to generate and output a second trip indicating signal indicating that the circuit breaker has performed a trip operation due to the occurrence of a low voltage on the circuit, by converting the second mechanical driving force received from the low voltage trip mechanism into an electric signal; a first driving force transmission mechanism (31, 33) connected between the first micro switch and the magnetic trip mechanism, and configured to transmit the first mechanical driving force from the magnetic trip mechanism to the first micro switch; and a second driving force transmission mechanism (37, 39) connected between the second micro switch and the low voltage trip mechanism, and configured to transmit the second mechanical driving force from the low voltage trip mechanism to the second micro switch, characterized in that the low voltage trip mechanism comprises an output plunger configured to output the second mechanical driving force, and wherein the second driving force transmission mechanism comprises a second lever rotatable to a first position contacting the second micro switch such that the second mechanical driving force output from the output plunger is transmitted to the second micro switch, and a second position separated from the second micro switch when the second mechanical driving force has disappeared. an over current relay configured to generate and output a first trip control signal when an abnormal current on the circuit has been detected, and to generate and output a second trip control signal when a voltage applied to the circuit has been detected as a voltage less than a predetermined reference voltage; a magnetic trip mechanism electrically connected to the over current relay, and configured to provide a first mechanical driving force when receiving the first trip control signal from the over current relay; a low voltage trip mechanism electrically connected to the over current relay, and configured to provide a second mechanical driving force when receiving the second trip control signal from the over current relay; a first micro switch configured to generate and output a first trip indicating signal indicating that the circuit breaker has performed a trip operation due to the occurrence of an abnormal current on the circuit, by converting the first mechanical driving force received from the magnetic trip mechanism into an electric signal; a second micro switch configured to generate and output a second trip indicating signal indicating that the circuit breaker has performed a trip operation due to the occurrence of a low voltage on the circuit, by converting the second mechanical driving force received from the low voltage trip mechanism into an electric signal; a first driving force transmission mechanism (31, 33) connected between the first micro switch and the magnetic trip mechanism, and configured to transmit the first mechanical driving force from the magnetic trip mechanism to the first micro switch; and a second driving force transmission mechanism (37, 39) connected between the second micro switch and the low voltage trip mechanism, and configured to transmit the second mechanical driving force from the low voltage trip mechanism to the second micro switch, characterized in that the low voltage trip mechanism comprises an output plunger configured to output the second mechanical driving force, and wherein the second driving force transmission mechanism comprises a second lever rotatable to a first position contacting the second micro switch such that the second mechanical driving force output from the output plunger is transmitted to the second micro switch, and a second position separated from the second micro switch when the second mechanical driving force has disappeared.