This study conducted comparison and data analysis of evaluation results from three kinds of monitoring methods for indoor air quality monitoring, which are Korean Official test method for indoor air quality, monitoring method by gas analyzer, and continuous measurement by using sensor. NO2, one of indoor air pollutants, was selected as a evaluation factor for this study because it is commonly generated during the operation of potable gas range. Monitoring results of NO2 concentration from three subjected methods show that background concentration of NO2, before operation of portable gas range, was 43.05~50.22ppb. On the other hand, NO2 concentration for four and half hours (4½) after gas range operation was 64.31~69.89ppb in average. Average concentration of NO2 during first thirty (30) minutes was increased about 33.85~49.39% than the concentration of NO2 before operation of gas range. In general, monitoring results by utilizing NO2 gas analyzer was 8.1% higher than the results by continuous measurement using sensor method. In case of monitoring method using sensor, the results was lower about 6.1% than Korean official test method, and lower about 11.7~3.2% than NO2 gas analyzer. Especially, change rate of concentration for first thirty (30) minutes measured by Korean official test method was 50ppb/hr, which is 44.4% lower than the change rate from NO2 gas analyzer, 90ppb/hr, and 43.2% lower than results from sensor, 88ppb/hr. In accordance with this study, it is concluded that monitoring frequency for indoor air quality management must be shorten during the time period having significant change rate of NO2 concentration. In other words, air quality monitoring must be considered characteristics of concentration changes as well as accuracy of measurement. Keywords : Underground, Indoor air quality(IAQ), NO2, Sensor, Portable gas range