PURPOSE: To easily fit a valve seat having excellent wear resitance in a valve box, by working the valve seat to the prescribed dimensions after padding a hard metal onto a valve seat plate and fitting it into the inserted hold of a valve box and finally welding the both.

CONSTITUTION: In case of manufacturing a valve, a valve box 1 and valve seat plate 10 are manufactured separately. The valve seat plate 10 is manufactured as follows; a recess part 9 is formed onto the surface of a valve seat blank 8 made of the same metal as the valve box blank 1 and a hard metal 11 having an excellent wear resistance is padded in the recess part 9. After working this to predetermined dimensions, the valve seat plate 10 is fit into the inserted hole 6 for the valve seat plate at the lower part of a vacant space 5 of a vertical branch 3 inside of the valve box 1 and the fitting circumferencial part is welded, and thus the valve box 1 and valve seat plate 10 are formed in one body. Since a surface of the valve seat plate 10 is covered by the padded part of hard metal, the wear caused by mechanical contact with a valve body is minimized and a service life of valve is prolonged.