PURPOSE: To obtain a clear-cut parting line after painting by treating the whole surface of a plastic molded article to be painted with plasma while the article is covered with a masking member.

CONSTITUTION: A masking tape 2 is stuck on the part 1 not to the painted of a material W to be painted, and treatment by plasma is carried out with a plasma treating apparatus to form a treated layer 12 on the whole surface excluding the part covered with the masking tape 2. The masking tape 2 is then released, and a masking jig is provided to the part not treated with plasma. A top coat is painted, baked, and dried, and then the masking member is released. Consequently, the parting line after painting is made clear, and the painting is performed rapidly and easily.