PURPOSE: To fill continuously and readily an active mass by filling a paste-like active mass under reduced pressure in a sleeve inside a reduced pressure container formed by mounting a core bar in the center along the long direction, and sealing the bottom.

CONSTITUTION: A paste-like active mass 10 obtained by for example, adding sulfuric acid and water to lead oxide and kneading them is put into a paste container 7, and a reduced pressure container 1 is exhausted from a suction hole 2. Thereby the active mass 10 flows down in a flowing-out tube 8 and is filled in a sleeve 5 gradually. When a filling amount reaches a specified amount, filling stops and other sleeve is replaced. Therefore, filling operation is continued.