PURPOSE: To eliminate a gap so as to prevent corrosion and contamination of supply water, due to staying water, by filling the air gap, generated between a valve unit and a valve seat member, with a seal agent.

CONSTITUTION: A valve seat member 16 is mounted into a mounting hole 17 formed in a valve unit 11, and a flange part 19, formed in the central part of the valve seat member 16, is fixed by a lip part 20 by calking. A gap, generated in the bottom of a tapered surface 18 in the bottom part of the valve seat member 16, and an annular gap, generated between the lip part 20 and the valve seat member 16, are filled with a seal agent 21. In this way, corrosion due to staying water and contamination of supply water due to corroded staying water can be prevented in the gap by its complete elimination.