An outer peripheral wall surrounds a heating chamber that communicates with an arc chamber through an opening that separates fixed contacts from each other in a circumferential direction. The outer peripheral wall includes a heat-resistive cylindrical heat-flow receiving wall portion that is arranged at a position opposed to the opening in a radial direction, and a cylindrical wall portion that is connected to the heat-flow receiving wall portion in a direction of a center axis and also connected to a fixed-side energizing member at its one end on the opposite side to where the wall portion is connected to the heat-flow receiving wall portion, and is made of an insulating material. With this configuration, the outer peripheral wall surrounding the heating chamber can be protected from damage and heat deterioration due to the influence of hot gas.