The present invention provides a nitrogen analyzing apparatus comprising: a nitrogen concentration measuring device configured to measure the concentration of an nitrogen impurities in a mixed gas including argon and oxygen as main components on the basis of emission intensity of a light emitted from the nitrogen impurities by an electric discharge in a discharge tube and an oxygen concentration of a sample gas introduced into the discharge tube, and a diluting oxygen-introducing device configured to add a diluting oxygen in the sample gas sampled from the mixed gas according to the oxygen concentration of the mixed gas.