An apparatus for introducing a pressurized gas includes a pressurized-gas supply-source, a plurality of measuring tanks, a first pressurized-gas supply-line, pressurized-gas supply valves in the first pressurized-gas supply-line, second pressurized-gas supply-lines and pressurized-gas discharge-control valves disposed in the second pressurized-gas supply-lines. A combination of the measuring tanks is determined on the basis of the amount of a pressurized gas required for forming a hollow portion in a molded article, and the pressurized-gas discharge-control valves disposed in the second pressurized-gas supply-lines are controlled on the basis of the above determination.
