PURPOSE: To move a valve body with a small driving force by fitting a penetrating means capable of circulating gas between a part cut off and sealed from a vacuum chamber of a valve body and a load lock chamber of the valve body.

CONSTITUTION: One surface of the valve body 3 faces the load lock chamber 2 and the other surface faces the vacuum chamber 1. A part having an area equal to or a little larger than the opening area of a valve seat on the side of the load lock chamber 2 facing the vacuum chamber 1 of this valve body 3 is cut off by bellows 8 from the vacuum chamber 1 and sealed with a packing 10 as a sealing device. The gas in the part cut off and sealed from the vacuum chamber 1 on the side of the vacuum chamber 1 of this valve body 3 and the gas in the load lock chamber 2 are communicated by a penetrating means 9 or a hole fitted on the valve body 3 and a force given to the side of the load lock chamber 2 of the valve body 3 and a force given to the side of the vacuum chamber 1 cancel each other to reduce the force given to the valve body 3. As a result, the valve body 3 can be moved by a small driving force.