To provide a pressurized gas introducing device which certainly introduces a pressurized gas with a constant pressure required to form a hollow part, and has a simple structure.

The pressurized gas introducing device is composed of: a pressurized gas feed source 10; a pressurized gas metering part 20; a first pressurized gas feed passage 30 for supplying the pressurized gas from the pressurized gas feed source 10 to the pressurized gas metering part 20; a second pressurized gas feed passage 32 for introducing the pressurized gas from the pressurized gas metering part 20 into the molten resin in the cavity provided in the mold; a pressurized gas feed valve 31 disposed between the pressurized gas metering part 20 and the first pressurized feed passage 30; and a pressurized gas discharge control valve 33 disposed between the pressurized gas metering part 20 and the second pressurized gas feed passage 32. The pressurized gas metering part 20 consists of a pipe.