Disclosed is a switching mechanism for a mold cased circuit breaker, capable of indicating a contacts status by a position of a handle. The switching mechanism comprises a handle; a lever providing a rotation supporting point of the handle; a shaft configured to rotatably support a movable contactor; a trip spring having an upper end supported by the handle, and configured to indicate a melt-adhered state of contacts by manipulating the handle to a TRIP position from an OFF position since a horizontal position of a lower end supporting point thereof in the TRIP position is discordant with a horizontal position of a rotation supporting point of the lever; a latch configured to restrict the trip spring; an upper link and a lower link; a toggle pin configured to support a lower end of the trip spring so as to provide the lower end supporting point; a latch holder; a nail rotatable to a position to restrict or release the latch holder; and an isolation lever having one end connected to the shaft and another end contactable to the nail, pressed by the lever by being upwardly moved so as to contact the lever, and configured to push the nail to a position to release the latch holder when manipulating the handle to an OFF position in a state that the contact of the movable contactor and the contact of the fixed contactor are melt-adhered to each other.