PURPOSE: To efficiently manufacture a small quantity of liquid nitrogen and nitrogen gas by a compact device by using the liquid level control in the dewer for manufacturing liquid nitrogen, using the nitrogen gas tank pressure for manufacturing nitrogen gas, and incorporating an unloader in a compressor for supplying material air.

CONSTITUTION: The nitrogen gas manufacturing device 6 uses a pre-processing device 4 or a membrane separator device 7. Nitrogen gas which is condensed more than 95% is stored in a nitrogen gas tank 9. Part of the stored nitrogen gas is delivered as a final product gas through a pipe 11, and the rest is supplied to a dewer 13 as a gas for liquid nitrogen. Liquid nitrogen gas is obtained by liquefying in the dewer 13 the gas for LN2 which is supplied from the nitrogen gas tank 9. The dewer 13 has a level gauge 20 for liquid nitrogen 16, and the liquid level is controlled by a reducing valve 15. This way, liquid nitrogen gas can be efficiently manufactured.