A producing apparatus of highly pure nitrogen gas which is used in electronic industry for manufacturing silicon semi-conductors. Conventional nitrogen gas producing apparatus of low temperature separation method and of PSA method are subjected to troubles frequently, the cost of the obtained product nitrogen gas is high, yet the purity is not very high. By the apparatus of this invention, the liquefied nitrogen storage means (23) is connected to rectifying column (15) through the inlet channel (24), the ultra low temperature compressed air supplied into the rectifying column (15) through the air compression means (9), removing means (12) and heat exchangers (13) (14) is cooled further by the evaporating heat of the liquefied nitrogen, the nitrogen is taken out in gas form by utilizing the difference in boiling point, and oxygen is left as liquid. The obtained nitrogen gas is combined with the gassified liquid nitrogen from the liquefied nitrogen storage means (23) and made into product nitrogen gas. Highly pure nitrogen gas can be produced at a low cost and with almost no trouble of the apparatus.