The number of schools, where air conditioners for cooling are equipped, has been rapidly increasing in Tokyo. Although most home has air conditioner in Tokyo, Pupils do not get used to school life exposed to air conditioned space in public elementary schools. The purpose of this study is to investigate the change of pupils behavior and corresponding indoor environmental change after installing cooling system into classrooms. Air temperature, relative humidity and CO₂ concentration were measured during summer season in twelve classrooms in an elementary school before installing cooling system and after installing. The investigated public elementary school is located in downtown Tokyo and has twelve classes, i.e., each grade has two classes. The questionnaire survey was conducted for investigating pupils perception and learning performance after installing air conditioner. The absenteeism survey was also conducted for health effect of air conditioned classroom.