To resolve a problem that the shape of a conventional feed water valve cannot be miniaturized because a diaphragm valve 20, a pilot valve seat body 40 and a pilot valve 60 are mounted in that order on the valve body 19 thereof having an inflow port 11, an inflow chamber 12, a main valve seat 13, an outflow port 14, and a second back pressure chamber outflow port 15.

A communication hole 17 between back pressure chambers for allowing the first back pressure chamber 43 side to communicate with the second back pressure chamber 44 side is formed in the valve body 19, and the pilot valve 60 and the diaphragm valve 20 are separately installed oppositely to each other.