To control cavitation trouble such as erosion by a means excluding charging.

A contour edge part of a valve element 14 or a contour edge part of a valve seat 18 is formed on a streamline shape same surface expanding over whole length in a direction of flow of fluid and plural slits 20 are formed on whole circumference of an end edge of the contour edge part. Break away of fluid from the contour edge part of the valve seat or the valve element occurs at a place close to the end edge of the streamline shape. Since the slits 20 are formed on the end edge, vortex cavitation based on break away of fluid occurs from inner parts of the slits (upper stream side) and moves to a tip along side edges of the slits and breaks away at halfway or from the tip. Vortex cavitation to occur from adjacent slits occurs at an interval of a pitch of the slits. It is hard for vortex cavitation to combine due to movement, break away at halfway or interval of slit pitch and combination growth can be controlled. Since combination growth is controlled, erosion, vibration and noise due to cavitation can be controlled.