To make a frame of flammable gas ignited by arc not to be propagated to an outside space of a case.

A flame extinguishment clearance that is set to have a gap size S for extinguishing a flame when the frame of flammable gas ignited by arc generated between a movable contact 24 and a fixed contact 14 is propagated toward a breathing hole 101 in a flame propagation route, is provided. With this, heat of the frame of flammable gas ignited by arc is deprived by a member to form the flame extinguishment clearance when passing through the clearance, thus, the frame is not maintained but it is distinguished.