PURPOSE: To form a disk of complicated shape from a material of low ductility by forming a domy convex part of a metallic plate in which the ratio of the diameter and radius of curvature is limited within specified range to specified dimension.

CONSTITUTION: A metallic plate 1 is so formed that the domy convex part 2 of diameter DO, radius of curvature ρ becomes 1/5≤ρ/D'O≤1. Next, the metallic plate 1 is placed on a supporting stand 5 with the convex part facing upward. The top of the convex part 2 is pressed by a punch 6 to form an outer peripheral part 7. At the same time, the center of the convex part is depressed to opposite side to form a concavity 8. The steel plate 1 on which a concavity 8 is formed is turned over and placed on a supporting stand 9. The top of the convex part 8 projecting upward is pressed by a punch 10 and an ornament part 11, a rib part 12 and washer base of nut 13 are formed roughly. This roughly formed disk is formed accurately by a male die and female die.