PURPOSE: To reduce generation of dendrite of a negative electrode in case of charging, and enhance charge-discharge efficiency by hardening an active material containing alkaline metal molded in a foil shape after it is exposed to a polymer electrolyte adjusting liquid without contacting with outside air.

CONSTITUTION: An active material 18 containing alkaline metal is put in a chamber 10, and is pushed out of a slit 12 arranged in a bottom part of the chamber 10 by a piston 11, and is molded in a foil shape. This foil-shaped molding is introduced into a polymer electrolyte adjusting liquid 14 filled in a tank 13 without contacting with outside air, and after it is pulled up through a roller 15 and a slit 16, an ultraviolet ray is applied from an ultraviolet lamp 17 to the molding, and the polymer electrolyte adjusting liquid 14 is hardened.