PURPOSE: To prevent generation of flapping and a multi-angle component, by specifying an angle against the mill center line by a line connecting the center of a centering roll and the center of a ring blank, extending from the rolling initial stage and the rolling middle stage to the end stage, respectively.

CONSTITUTION: A part of a ring blank A is pinch-held in the radial direction by a main roll B and a mandrel roll C, the mandrel C is moved, the ring blank A is thinned by gradually narrowing a space against the main roll B, and its outside diameter is made large. In this case, at the rolling first stage, a centering roll E is supported at position where an angle made against the mill center line by a line connecting its center and the center of the ring blank A becomes 90 degrees. Also, in case of the rolling middle stage through its end stage, it is moved so as to make an angle between 72 degrees and 90 degrees, or 90 degrees and 120 degrees (provided that 72 degrees, 90 degrees and 120 degrees are not included).