<p>A power usage calculation system wherein a data management system to which a plurality of power meters for totalizing the amounts of power usage by electric appliances are connected is connected with an energy management system via a network, and a plurality of first partial information are calculated by use of the amounts of the power usage totalized by the power meters and stored in a plurality of storage servers. The plurality of storage servers each calculates second partial information using a plurality of pieces of the first partial information relating to the amount of power usage totalized by each of the power meters, and transmits thereof to the energy management system. The energy management system receives each piece of the second partial information transmitted respectively from the storage servers and, using thereof, calculates the total of the amounts of the power usage totalized respectively by the power meters.</p>
