A switching mechanism of a circuit breaker includes a case, a handle rotatably coupled to a side plate fixed to the case, a U-pin coupled to a lower portion of the handle, a lever coupled to the U-pin, and a crossbar disposed in a mounting portion protruding from the case to be perpendicularly movable, the crossbar being moved by receiving contact pressure of the lever, wherein the lever is provided with a contact pressure portion formed in a curved surface on a lower surface thereof, to press the crossbar perpendicularly downward upon closing a circuit.