A method includes a step of applying an aqueous 2-package type first colored paint to form an uncured first colored coating film; a step of applying an aqueous 1-package type second colored paint to form an uncured second colored coating film; a step of applying a solvent-based 2-package type clear paint to form an uncured clear coating film; and a step of heating the uncured first colored coating film, the uncured second colored coating film and the uncured clear coating film to 75 to 100° C. to simultaneously cure these films. The solvent-based 2-package type clear paint contains a hydroxyl group-containing acrylic resin and a polyisocyanate compound in a ratio of 1.5 to 2.0 equivalents of isocyanate groups in the polyisocyanate compound relative to 1 equivalent of hydroxyl groups in the hydroxyl group-containing acrylic resin.