The method according to the present invention comprises: a first curving step of curving a plate-like metallic blank (1) such that the blank (1) is convexed; a bending step of bending, with the outer peripheral edge portion (1e) of the blank (1) restrained from radially outwardly extending, the resulting arcuate portion (1b) of the curved blank (1) in the direction opposite to the convex direction thereof, so that a boss (6) is formed; and a second curving step of pushing the inner peripheral portion of a flat portion (5) of the blank (1) in the direction opposite to the boss projecting direction. Through the steps above-mentioned, the blank (1) is provided at the center thereof with the case-like boss (6) projecting in one direction from one lateral side of the blank (1) and at the outer periphery thereof with a peripheral wall (7) projecting in the same direction in which the boss (6) projects. Thus, with a small press machine, there can be securely formed, with high precision, a boss having a desired diameter and a desired projecting height, without the original thickness of the blank (1) decreased so much in the course of production steps.

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