PURPOSE: To apply complicated relief patterns such as woodgrain patterns to the surface of a moving thermoplastic resin molded article, by extruding a thermoplastic resin through an extrustion die furnished with a particular rotating element in the die lip.

CONSTITUTION: As element 3 having a plurality of through-holes 4 and rotating with a gear 6, is mounted in the die lip 2 of an extrusion die 13. A thermoplastic resin molded article 12 extruded from the other extrusion die 9 is transferred with a take-off mechanism 11 through a sizing die 10. The molten or softened thermoplastic resin extruded intermittently through the extrusion die 3 adheres to the surface of the molded article 12 to form relief patterns on the surface. The shape of the pattern is determined by the shape of the through-holes 4 of the element 3 in the extrusion die 13.