Reducing the energy used in Cloud Computing is an important issue a sustainable society. There are many existing approaches for reducing energy use in data centers, but new approaches are needed in case of energy management of Cloud Computing. Cloud Computing involves decentralized data centers, so new flexible way for collecting energy consumption data becomes quite important. Many current approaches focus on reducing energy consumption by air handling equipment, however energy from IT resources also need to be optimized for a total energy management of Cloud Computing. For advanced energy management for Cloud Computing, we developed a Cloud energy management system with sensor management functions, with an optimized VM allocation tool to minimize energy consumption at multiple data centers. Our evaluations showed more than a 30% energy savings for the servers in our experimental environment. Our system can be extended to optimize energy usage from various perspectives, such as for minimizing electricity bills or carbon emissions. © 2013 IEEE.