To maintain perfect sealing function so that crack or the like is not generated on a bellows even in the use for a long term.

This valve is constituted so that an expansible bellows 40 is stuck fast to a valve stem 23 at the one end and to a valve cover 17 at the other end, for preventing liquid from leaking through the position where the valve stem 23 penetrates through the valve cover 17. In this case, the bellows 40 is fitted so as to become in the natural length in the condition of valve opening. For preventing displacement of the bellows 40 in the lateral direction, a guide slidingly contacting with the inner circumferential face of a valve box extending cylinder 15 is provided on the way of the bellows 40. The bellows 40 is an omega bellows made of inconel alloy.