The environment has played a key role to improve the living condition and develop the scientific industry. In building industries, we should consider the environment and mitigate the environmental affect. For mitigating its affect, various areas of building technologies have been developed and applied into the filed work. In addition, the process in applying into field would require to conduct the assessment of the environmental affect and improve its applied technology. A lot of assessment methods have been proposed in evaluating the building condition such as post-occupancy evaluation, life cycle management and life cycle assessment. Among these assessment methods, life cycle assessment is effectively utilized the environmental affect during the building life cycle. Therefore, this paper aimed at analyzing the energy consumption and CO2 emission during the building life cycle, using the life cycle assessment and application of the example in apartment housing. This study shows that the maintenance and the production of building materials stage shares most of the amount of the energy consumption and CO2 emission and directly plays an important role to planning the building in terms of the life cycle. Second, the other stages bring about a very small amount. It is important to decide the building shape and contents to mitigate the environmental affect in terms of material, volume, the pattern of the energy use and others.