In this study, the reduction performance of PM2.5 and chemicals was evaluated when the ventilation device and air cleaner, which are representative air cleaning devices for apartment complexes, were operated individually or simultaneously. The clean air delivery rate (CADR) was highest when the ventilation device and air cleaner, were operated simultaneously. When each device was operated individually, the CADRs of the air cleaner, were higher than that of the ventilation device in all cases except CO2. The energy efficiency of the air cleaner was much higher than that of other devices. This is because the power consumption of the air cleaner, is relatively low compared to that of the mechanical ventilation device and its CADRs are high.