A continuous measuring system for atmospheric O2/N2 ratio was developed employing a paramagnetic oxygen analyzer. Sample air is allowed to flow through a water trap cooled to −80°C, and is introduced into the analyzer at a flow rate of 100 mL min−1 by stabilizing the pressure to an order of 10−1 Pa. The analytical reproducibility of the O2/N2 ratio achieved by the system is about 5 and 3 per meg for 2 and 30 minutes average values, respectively. The O2/N2 ratio values obtained by the system are in good agreement with the values obtained by our traditional system using a mass spectrometer. Using our new system, we started measuring the atmospheric O2/N2 ratio at Minamitorishima, Japan since December, 2015. Some preliminary results show clearly the O2/N2 day-to-day and seasonal variations that are in the opposite phase with the CO2 concentration.