Abstract: A multipole circuit breaker of a type with a mechanism pole having a switching mechanism in which adjacent poles are disposed in opposition to the mechanism pole with an interphase wall therebetween and each having an internal attachment such as an alarm switch or the like but no switching mechanism. A latch engages a cradle of the switching mechanism and is arranged to be actuated by an automatic tripping device. A supporting shaft rotatably supports the latch, an a lever fixed on the supporting shaft engages the cradle. Actuators are fixed on the supporting shaft so as to engage the internal attachment of the respect adjacent poles. The supporting shaft is made of metal. Insulating caps are inserted and fixed onto end portions of the supporting shaft, the supporting shaft passing at portions of the insulating caps through the interphase walls. The actuators are inserted and fixed onto the insulating caps.