A pair of arcing contacts 3 and 5 facing each other are placed in a tank 1 to perform opening and closing operation, and a puffer cylinder 7 is coaxially provided on the circumference of one arcing contact 5. A puffer chamber 9 is comprised of the puffer cylinder 7, a fixed piston 6, and a hollow rod 8. An insulating nozzle 4 forming a space communicating with the puffer chamber 9 is provided. An exhaust tube 2 for exhausting and cooling hot gas discharged from an arc produced in the insulating nozzle 4 is provided on the circumference of the other arcing contact 3. A structure 11 for temporarily reducing the flow path area is provided on the inner circumferential surface at short of the end portion of the exhaust tube 2.