PURPOSE: To enable a dense and uniform base body of a lead alloy free from cavities to be formed by providing a mechanism of reducing the pressure in molds in pressure-casting of lead alloy by using a compressed inert gas.

CONSTITUTION: In casting of a base body or the like for plates of lead storage batteries, a molten lead supply port 9 is held closed by a valve 8 while molten lead 4 is being pressurized by a pressurizing part 7. Hence, the molten lead does not back flow into a melting pan 1 and is pressure-cast in the die 13 fixed to a frame 12 from a nozzle part 11 through a molten lead supply pipe 10. At this time, the pressure in the die 13 is beforehand reduced in a reduced-pressure chamber 16 by compressed air 15, and at the same instant when the molten lead 4 is pressure- injected and forced into the mold 13, a solenoid valve 17 is opened to exhaust the air in the mold 13. Thus, the air in the cast base body goes nill, and the substitution of the air with the molten lead 4 is smooth and stable, and this makes possible the casting of good base bodies.