The circuit breaker according to the present invention comprises: a pair of contact mechanisms for switching a pair of circuits; a switching mechanism for driving the pair of contact mechanism to a circuit opening position or a circuit closing position; a trip bar rotatable to a first position for latching the switching mechanism or to a second position for releasing the switching mechanism; and an instant trip mechanism for pressing the trip bar to rotate to the second position, wherein the instant trip mechanism comprises a pair of armature assemblies and movable to a position for pressing the trip bar to rotate to the second position; and a pair of electromagnets provided to face the pair of armature assemblies and applies a magnetic attractive force to the pair of armature assemblies in response to the fault current on the circuit requiring an instant trip.