PURPOSE: To mass produce by the simple operation without degrading the straightness and revolutional balance of the worked product, by holding the material with the circumferentially grooved die segments, and by forming the annular projection in the circumferential surface of the material using the bulging roller.

CONSTITUTION: The material 6 is quietly held by the segments 7 provided with the circumferential groove 8, and then, the driving mechanism 2 is driven; hereby, at the same time as the rotary shaft 3 rotates, the rotary shaft 12 also independently rotates slowly; as a result, the eccentric gear 13 integrated with the gear 12 turns around the eccentric disk 11. The respective bulging roller 9, being set circumferentially in the side plane of the eccentric disk 11, moves radially outward and presses the inner surface 6a of the material 6, and also, makes the rotation around the axis of itself and the revolution around the rotary main shaft 3. Hereupon, as a result of collaboration of respective bulging roller 9 and the circumferential groove 8, the annular projection 6b as the circumferential bank is formed without damaging the straightness of the worked product.