Recently, global warming becomes one of the most serious problems for sustainable development in the world and energy saving is now important activity as the countermeasure. In industrial sector, the energy saving in not only factories but also increasing office buildings is required. In this paper, BEMS(Building and Energy Management System) which totally manages energy consumption and generation in whole office building is first introduced, then the activity for improving office work productivity by controlling office light is explained as one of the examples for positive energy saving activity.