An improved circuit breaker includes an arc extinction system having one or more insulators that generates a desirable gas in the presence of an arc. The unit cells are disposed in the housing on a slant at a predetermined angle with respect to an inflow of the coolant. The amount of the second dopant is greater than the amount of the first dopant. One of the guide portion and the developer conveying portion has a contact portion that causes the guide portion and the developer conveying portion to partially contact each other in such a manner that a gap is partially formed therebetween.