Method for manufacturing metal container, apparatus for manufacturing metal container, and metal container

A method for manufacturing a metal container, comprising:

• a first step of forming a substantially planar four-sided bag using a metal plate;
• a second step of sandwiching, by first and second parallel plate jigs, one surface and the other surface of the four-sided bag formed in the first step;
• and
• a third step of forming, using the four-sided bag, a container having a substantially truncated square bipyramidal shape or a substantially rectangular parallelepiped shape by pressurizing an inside of the four-sided bag while maintaining a contact state by the first and second parallel plate jigs with respect to the four-sided bag sandwiched between the first and second parallel plate jigs in the second step, and expanding a volume space in the four-sided bag while increasing a distance between the first and second parallel plate jigs.