The method, in which base material ingot 1 is heated and softened in an electric furnace 3, drawn with a pair of pinch roller 6 and 6, and elongated to make base material rod 7 having a smaller diameter than the ingot, features: forming either a roller groove 11 having a curvature radius which is larger than the outer diameter of the base material rod 7 or a V-shaped roller groove 11 having the cross section consisting of straight lines on the surface of the pinch roller 6 made of metal; nipping with the facing roller grooves 11 and 11 respectively formed on the surfaces of a pair of said pinch rollers 6 and 6; and drawing said base material rod.