To prolong a life in a hard surface while a coating time is shortened by a method wherein a principal coating surface is regarded as one coating surface without dividing the principal coating surface into a plurality of surfaces, at first a coating surface of a reinforcing member is coated over all the length in the length direction, and an idle transfer distance between the coating surfaces is set to the shortest one.

A side surface of a web WE being a principal coating surface is regarded as one coating surface without dividing that into a plurality of surfaces with vertical ribs VR1-VR4 and horizontal ribs UHR, DHR, at first the coating surface of the same surface vector is selected among respective upper and lower coating surfaces of upper and lower faces UF, DF, vertical ribs VR1-VRH, and horizontal ribs UHR-DHR, the coating surface of the same vector is classified by groups, and they are coated over all length in the length direction. Herewith, an idle transfer distance between the coating surfaces from a coating end point to a coating start point even in those groups is set to shortest one. Thereby, all the coating time can be shortened, pivoting of a wrist part of an articulated robot can be minimized, and a life in a hard surface can be prolonged.