PURPOSE: To improve the adhesion of a paint film to a resin member by subjecting primer coating on the member to surfacer coating with two-pack urethane coating and by carrying out baking and drying at a low temp. or catalytic curing.

CONSTITUTION: A resin member 1 is washed, coated with polyolefin resin-based primer paint having ≤-40°C glass transition temp. and further coated with two-pack urethane paint. The paints are baked and dried at a low temp. of about <80°C to form a polyolefin resin primer layer 2 and a urethane surfacer layer 3 on the surface of the resin member 1. The layer 3 is then coated with color paint for a steel sheet such as melamine-alkyd resin paint and this coating is baked and dried at a high temp. of about 130-150°C to form a top coating layer 5 on the surface of the layer 3.