The purpose of this study is to quantify the total amount of energy consumption and CO2 emission caused by the construction, operation, maintenance, and renovation of office buildings in Japan. In order to quantify the life cycle energy consumption and CO2 emission of a building, it is necessary to obtain an estimate of the total quantity of domestic products and services used directly or indirectly (including the repercussion effect of the economy) during the life cycle of the building. The Input/Output (I/O) Table of Japan is used to calculate the total domestic product and then energy consumption and CO2 emission are estimated by using energy consumption and CO2 emission data for unit production of various categories of industries.