PURPOSE: To prevent oxidation of cadmium active substance and deterioration of its electrical characteristics, by establishing an inactive environment in which the drying process is applied to the plate drawn-out from a formation tank.

CONSTITUTION: The band-shaped negative electrode original plate 1 wound in a coil form is introduced into a formation tank 3 continuously, guided by an electricity feeding roll 2 which serves also as guide rails. The negative electrode original plate 1 is charged in negative potential by the electricity feeding roll 2, and shifts the formed opposite electrode 4 arranged in the formation tank 3 and charged in positive pontentially, and converts the cadmium oxide on a paste-form cadmium negative electrode to metal cadmium. After being introduced into a dealkalization tank 7 containing water or weak acidic liquid 6, the metal cadmium is subjected to the formation and drying process accomplished by means of the heat source 8 in a drying furnace. In this drying process, the plate in wet state is dried in inactive environment containing inert gas such as nitrogen, and thus cadmium active substance can be prevented from oxidation.