It is an object to reduce the time and cost for manufacturing a spherical tank compared to conventional methods. A method for producing a polygon having a plurality of Pentagon flat plates and a hexagonal flat plate, the method comprising: Preparing a polygon having a connection portion that penetrates through the flat plates and connects a sealed space inside the polygon to an outside of the polygon, the polygon having a plurality of Pentagon flat plates and a plurality of hexagonal flat plates, A deformation step of deforming the polyhedron (11) into a spherical tank (21) by applying pressure to a sealed space inside the polyhedron (11) through the connection part (6), And (2) a step of forming a spherical tank on the surface of the base material. Figure 1

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