An energy management apparatus is used to manage energy to be supplied to a system. A paid energy resource can be supplied to the system from the outside. The system is provided with two or more functional device units realizing a specific function using the input energy and adapted to satisfy an external request using at least one of the two or more functional device units such that supply of energy to the functional device units can be controlled. In the apparatus, a normalizing section normalizes input energy of each of the two or more functional device units in terms of the cost of the paid energy resource required for producing the input energy. In addition, a determining section determines to which of the two or more functional device units a predetermined quantity of energy should be fed such that the cost incurred in the system can be reduced.