To further improve reliability and long-time stability of a stellite thick part by welding a Co alloy to form a thick part for providing a burning resistance and a wear resistance to the sliding part of each of various valves and executing ceramic coating on the thick part for mending this valve thick part.

For mending the stellite thick parts 3a and 3b of a valve body 1 made of stellite and the stellite thick parts 4a and 4b of a valve box 2, ceramic coating layers 6a, 6b, 7a and 7b made of CrN or the like are respectively executed on thick metals as a last mending stage. The ceramic coating layers 6a, 6b, 7a and 7b are excellent in wear resistance and erosion resistance and thus the reliability of the valve thick part is improved. Also, if the stellite thick parts 3a, 3b, 4a and 4b of the valve body 1 and the valve box 2 are damaged, the damaged parts are mended and then ceramic coating layers 6a, 6b, 7a and 7b made of CrN or the like are executed on the mended parts.