Abstract: A circuit breaker comprises a container made of electrically insulating material, the container being constituted by a casing and a cover; a switching mechanism contained in the container; partition walls defining a recess in the casing, the recess being separated from an interior of the container by the partition walls; and a base made of electrically insulating material, on which an accessory which is in the form of a cassette is detachably mounted, the base being detachably mounted in the recess formed in the cover.

Abstract: The present invention is directed toward a circuit breaker having an open-and-close shaft; holding member coupled to the open-and-close shaft; at least one movable contactor coupled to the holding member; support member for rotatably supporting the open-and-close shaft; and stopper member coupled with the support member so as to restrict an open-and-separation position of the movable contactor, wherein the circuit breaker is disposed within a case, the stopper member are formed on side faces of between-phase partitions of the case and a portion of the holding member contacts the stopper member. Thereby, it is possible to improve an insulation function and to lessen the impact between the holding member and the stopper member.