PURPOSE: To prevent a pressure seal ring from being wedged by providing the pressure seal ring to be arranged in a pressure seal ring groove between a valve guide ring and a valve body before the valve guide ring is attached to the valve body.

CONSTITUTION: A valve element 11 moves in a hole 12 in a bonnet cylinder of a bonnet cylinder 13. A pressure seal ring 14 moves in a circumferential groove 15 extended around an outer surface of the valve element 11 and slides for adjacent contact surfaces of a wall 17 of the hole 12 in the bonnet cylinder. A pressure seal ring 43 to be arranged in a pressure seal ring groove 41 between a valve guide ring 45 and a valve main body 47 is provided before the valve guide ring 45 is attached to the valve body 47. It is possible to prevent the pressure seal ring from being wedged in this way.