PURPOSE: To enhance properties of interlaminar adhesion by adding a specific bonding additive to at least either of two kinds of films in the formation of a two-tone coat film of coating composition containing melamine resin.

CONSTITUTION: For primary coating compositions and secondary coating compo sition, heat curing type coating material comprising acryl-melamine resin, alkyd- melamine resin, polyester-melamine resin and the like as base resins are used. In said process, to either or both of coating compositions, a bonding additive composed of at least either of a compound having hydroxide as derivative of high class fatty acid such as stearic acid, palmitic acid, oleic acid or the like, or a compound consisting of reacted diamine such as hexan methylenediamine or triamine, is added by 0.1W5wt% in total nonvolatile content of coating composition.