PURPOSE: To alleviate drive force and to downsize a drive mechanism by providing a stabilizer projecting to the downstrem flow path from the center axial part of end wall facing the down stream side flow passage at the time of full closing of a main valve body and having a flange part with its peripheral part projecting in the direction of increasing diameter.

CONSTITUTION: When a main valve body 31c is opened, high pressure fluid is flowed from an annular gap between the body 31 and a valve seat 4 strongly. Force is thus generated to raise the body 31 in the valve opening direction, to the bottom wall of the valve body 31. At the simultaneous time, the force collides on the upper face of a flange part 32b of a stabilizer 32, and the force generates force to close the valve 31 downward so that raising force is cancelled. As a result, while a pilot valve body 5 is maintained its open condition still after the closure of main valve body 31, the main valve body 31 is raised through the engagement of a valve seat 7 with a stopper 9. Consequently, it is thus possible to make the size of the mechanism 21 small and compact and reduce costs without application of valve closing force to a drive mechanism 21, and with a required drive force lightening effect of the drive mechanism 21 by the pilot valve body 5.