In spring and autumn, the natural ventilation is effective in not only the ventilation but also the thermal environment control. However, it is difficult to maintain the indoor thermal comfort when the enthalpy of the outdoor air is higher than that of the indoor air. Then, the hybrid air-conditioning, which is the combination use of the natural ventilation and the air conditioning, is available too. The purpose of this study is to reveal the indoor thermal environment by the natural ventilation and the hybrid air-conditioning. In this paper, the results of the measurement in the actual building in last autumn and the results of the CFD simulation are shown.