PURPOSE: To reduce an amount to be cut and to improve the yield of material by carrying out a stage for obtaining a preform in the shape of a thick-wall ring from metallic stock, a stage for obtaining a thinned secondary preform and a stage for obtaining a forged part in the shape of a thin-wall cup in sequence.

CONSTITUTION: Metallic stock is set in the cavity of a preforming die to obtain the primary preform 51 in the shape of a thick-wall ring and having a central hole. Then, a annular secondary preform 60 having a tapered part 61 surrounded in the peripheral direction is obtained with a rolling mill composed of a mandrel roll and a profile roll. A 1st upper die and a punch are lowered at the same time as the secondary preform 60 is set in the forming cavity of a lower die assembly. The shoulder part of the 1st upper die clamps the tapered part 61 of the secondary preform 60 in the thickness direction and presses it strongly. The thickness part of this tapered part 61 is expanded inward and extruded backward. The thin-wall cup shaped forged part is obtained through these stages.