PURPOSE: To provide mechanically and thermally excellent characteristics by applying a hardened layer by powder buildup welding on a seat part formed to be opened in a conical shape on one of holes of a thin ring seat main body in uniform thickness.

CONSTITUTION: A seat material 50 of heat resistant steel is formed roughly in the same shape as a valve seat 10 by forming it by precision forging such as cold forging, full enclosed die forging, etc., or by precutting a pipe material at the time of manufacturing the valve seat 10. That is, a hole 52 is formed in the inside of a thin ring material main body 51, and a roughly flat tapered surface 53 is formed on a part corresponding to one seat part of the hole 52. Thereafter, powder buildup welding is directly and thinly applied on the tapered surface 53 of this seat material 50 by degreasing, etc., as required. Thereafter, the material main body 51 is machined and finished by cutting it along a dashed line and cutting a buildup part 54 in a conical shape. In this way, a tapered hardened layer 55 is formed on a seat part 13, for example, in thin and uniform thickness of one milimeter, and its durability is improved.