High purity O2 concentrated by the PSA-type O2 separator was applied to a room ventilation system combined with CO2 adsorption module to remove the indoor CO2 for the indoor air quality. And then the room was occupied by several persons to breathe for the O2 consumption and CO2 generation. As a result, the indoor air quality was improved by the ventilation system combined with the O2 supply and the CO2 adsorption module. It was due to the fact that the CO2 concentration was not steeply increased, but also even decreased and then the increasing rate of the O2 concentration with the O2 supply was simultaneously increased by the CO2 removal despite the CO2 generation and O2 consumption with the four persons’ breathing. As a representative result, in the case of supplying the high purity O2 of 30 L/min under using the CO2 adsorption module, the best performance with the highest increasing rate of O2 concentration and the lowest increasing rate of CO2 concentration was obtained among the various cases, and then the increasing rates of CO2 concentration and O2 concentration were -2.3 ppm/min and 33.3%/min, respectively.