An inline-ready method of finishing the surface of a long material (W) capable of preventing any environmental problem from occurring and the mechanical properties of the long material from deteriorating, comprising the steps of holding the long material (W) by two or more elastic endless belts (1) with a specified force, rotating the elastic endless belts (1) in the same direction as or in the reverse direction to the moving direction of the long material by moving the long material (W) and increasing or decreasing the rotating speed of the elastic endless belts (1) more than or less than the moving speed of the long material, and loading powder and granular grinding material (S) between the elastic endless belts (1), characterized in that the grinding material (S) is moved relative to the long material (W) to rub the grinding material (S) against the long material (W) so as to finish the surface of the long material (W).