The manufactured pieces are the ones both end surfaces thereof in the tire circumferential direction are cut from the pieces before cutting 1 and the pieces before cutting 1 have the cutting regions whose cross-sectional shapes in the tire width direction are the same at both ends of its circumferential direction. And in the cutting process of cutting the pieces for modifying the lengths in the circumferential direction from each of the pieces before cutting 1, in order that the length in the tire circumferential direction of each piece after cutting and that both of the end surfaces in the circumferential direction of the piece after cutting are included in the cutting regions, the cutting lines of each piece are set at different not less than two positions (a, a′ and b, b′) in the tire circumferential direction and the pieces are cut by either one of the set cutting lines.