PURPOSE: To reduce the abrasion of an operational mechanism sliding part, so as to obtain stable operational characteristic by defining a neutral line that crosses with a moving lead rod shaft center line at right angle, as 1/2 in the side of a vacuum valve, and 1/2 in the side of a reverse vacuum valve.

CONSTITUTION: An opening distance 16 is divided into two by the rotational point 4a of a rotational shaft of an operational mechanism, and the center is provided on the line that crosses with a moving lead rod shaft center 2a at right angle. An estimated abutting point 11' passes a contact opening starting point 13 as well as an opening route point 14 on the moving lead shaft center 2a, and is provided on a completely closed route point 12 on an arc around the rotational point 4a of the rotational shaft as a center. A supporting point 10 is provided in the side of a vacuum valve from the divided point of the opening distance 16, on the same arc, namely at a 1/2 point of the amount of wiping 15 plus the opening distance 16. The supporting point 10 is constantly in the reverse vacuum valve side from the estimated abutting point 11' thereby. Stable operational characteristic is thus obtained without generating friction between a moving lead rod guide and the moving lead rod 2.