To provide: a convenient and economical metal plate press-forming step with a fine line pattern, capable of forming a fine line simultaneously with forming a housing; a press-formed metal housing thereby; and a method of forming a fine line of a forming die.

Firstly, a metal plate is placed in a forming device. The forming device includes a sealing die and a forming die. The forming die has a surface of a housing shape, and the surface includes a first fine line pattern formed by the etching. Secondly, the metal plate is heated and applied with the gas or liquid pressure in several stages to be tightly pressed against the surface of the forming die, and the first fine line pattern is pressed to obtain a second fine-line pattern. Thereafter, the press-formed metal plate is punched to obtain a press-formed product.