PURPOSE: To clean the surface of a back-up roll adjacent to a coating head, by arranging a doctor blade and a suction part to suck a coating agent scraped by the blade.

CONSTITUTION: A workpiece 1, to be coated, is carried along an arrow 3 around a back-up roll 2 and coated by a coating head 4. An excess amount of a coating agent, which passes through the workpiece 1, to be coated, and adheres to the back-up roll 2, is scraped by a doctor 6 attached to a coating device with a support 5 and introduced through a suction opening 7 into a suction part 8. In this way, the excess amount of the coating liquid adherent to the back-up roll 2 is easily removed, so that its adhesion amount to the back-up roll 2 is neither raised nor broken away. Consequently, the controlled running condition of the workpiece, to be coated is not hampered, and the contamination of the workpiece, to be coated, can be inhibited.