Abstract: A circuit breaker having a safe construction, where no electrically charged portions are exposed in an accessory installation area or anywhere outside a main circuit case even if a cover of the circuit breaker is opened in a live condition. In order to achieve above object, the circuit breaker of this invention includes the main circuit case made of an insulating material, and an opening-closing trip mechanism disposed outside of the main circuit case and electrically insulated from the main circuit. According to this invention, a circuit breaker capable of eliminating the risk of an electric shock, thereby providing the excellent safety can be obtained.