To solve the problems that the function capable of supplying a large volume of high pressure gas is demanded for a high pressure vessel; valve in a short time; the high pressure vessel valve having a flow coefficient Cv applicable for the system does not come in practice; and the automation of a flow control is greatly needed.

The problems can be solved by comprising a seat structure having (1) a projection of a circular truncated cone shape (sommma shape) having a recess of a in height, and D in diameter with a recess of b in depth, and having a top end r surface is formed in a seal part of a seat disk forming the seal part at a drain cock 1 side. (2) In the seal part of the seat disk 5 placed in contact with a valve main body side 3, a contact diameter D and the diameter d of a gas flow inlet 2 of the valve main body 3 are always D>d.