PURPOSE: To prevent growth of a deep flaw, etc., on a machined surface by polishing an outer surface of an aluminium pipe by using an elastic polishing tool containing abrasive grains Young's modulus of which is lower than the aluminium pipe and thereafter, by treating the outer surface of the aluminium pipe with roller varnishing.

CONSTITUTION: An aluminium pipe 11 is polished by installing an elastic polishing tool containing abrasive grains on a grinding wheel 14. At the time of this polishing, polishing is carried out by properly selecting the grinding wheel 14 and the aluminium pipe 11 in the same direction or in the opposite directions by a rotational drive means and rotating them. As this polishing goes on, the abrasive grains on the surface of the grinding tool retreat by reaction force from the aluminium pipe 11, the surface of the polishing tool evenly polishes the aluminium pipe 11, and it never make local deep flaws. The aluminium pipe 11 polished in this way is varnished and finished by a roller varnishing device.