A rotary tool (140) is relatively moved against members (30, 30) to be welded so as to perform friction stir welding of said members, while blades (145) mounted on the rotary tool (140) and a rotary brush (220) are used to cut the welded portion, and swarfs on the cut surface are removed through a suction opening (225), before medium liquid is supplied on said cut surface through a supply opening (240). Next, an inspection roller (250) is rotated on the surface of the welded portion for inspection. A probe (251) is provided within the roller (250). Upon detecting a defect, paint is applied to the position of defect by a marking device (270). Thereafter, based on said marking, the joint portion is cut and repaired by welding.