PURPOSE: To form easily and surely a parting line on a product having an intricate shape by interposing a strippable paint which permits cut stripping on the surface of a resin product.

CONSTITUTION: A release agent 12 such as silicon is coated on a mold on the surface wherein a painting surface of a resin product (a) is formed, and a strippable paint 13 formed by compounding toluene, methyl ethyl ketone, stabilizer, etc. with vinyl acetate or vinyl chloride is coated thereon over the entire surface and is dried. A top mold coated with the similar stripping agent on the surface is superposed on said mold, and a resin is injected into the mold, whereby the resin is molded. After the strippable paint 13 on the resulting product (a) is dried, the paint is cut and stripped by a suitable means, and a painting surface part 16 is formed. The part 16 is then subjeced to painting, drying, baking, etc. and the paint 13 in the other part is stripped, whereby the product (a) is completed.