To further develop an Itro treatment method for the metal surface modification.

In the production of a facing crown in dental treatment, at first, for forming fine ruggedness on the surface of a cast gold-silver-palladium alloy 2, sand blasting treatment (S11) is performed, and thereafter, an oxide film is formed on the surface of the gold-silver-palladium alloy 2 using flame (S13). Next, by performing an Itro treatment of spraying flame on the surface of the gold-silver-palladium alloy 2 using a gun type gas lighter mounted with a cylinder charged with a silane compound and a propane gas, silicon hydroxide is formed on the oxide film (S14). Then, after the application of a primer and an opaque agent, a hard composite resin is built-up (S15, S16).