The inspection of the grasp of the energy use actual situation and the effect of the latest energy system in the large-scale and heavy used office building is the important knowledge to plan the energy system of the future office building. The purpose of this study is to verify the realities of the energy consumption and the thermal loading by using the BEMS data of the latest, large-scale office building with the highly efficiency gas engine cogeneration system and to verify the effect of the cogeneration system.