Indoor air pollution caused by the chemical substances such as formaldehyde and volatile organic compounds (VOCs) is a serious problem in Japan. Even if the emission rates of chemical substance are small, the concentration shows a tendency of high levels due to the increase of the air-tightness in residences. Bake-out might be a novel approach to reduce formaldehyde or VOC levels in a new residence. Bake-out is based on the theory that vapor pressure from building materials will be increased by elevating temperature in rooms. Some quantitative reports on bake-out are indicated by J. R. Girman et al.. But, in these reports, we can't find useful information which is related to Japanese construction method. So, this study was carried out to determine the effectiveness of the bake-out practice on VOC or formaldehyde concentration.