A metallic material containing both a second constituent and a third constituent having positive and negative heats of mixing relative to a first constituent, respectively, and including a compound, an alloy or a nonequilibrium alloy having a melting point that is higher than the solidifying point of a metal bath made of the first constituent is placed in the metal bath. The metal bath is controlled to a temperature lower than a minimum value of a liquidus temperature within a range of compositional variations in which the amount of the third constituent in the metallic material decreases down to a point where the metallic material becomes substantially the second constituent so that the third constituent is selectively dissolved into the metal bath.