In order to estimate cooling loads in dwelling, it is important to assume the occupants air conditioning ON control behavior. We surveyed the usage of air conditioner in living rooms and bedrooms to study the relation between thermal environment and ON control. As a result, it was supposed that in the bedtime, occupants require high quality indoor thermal environment and make ON control customarily. Moreover, it was found that the indoor temperature at the time of ON control has a relation to the setting temperature of air conditioner.