If the energy service enterprise is responsible for paying costs for applying energy-saving measures to the object facilities, measures the energy consumption after taking the energy-saving measures, calculates the amount of curtailed energy cost by comparing the measured value with the energy consumption before taking the energy-saving measures previously stored in the database, and receives at least a part of the curtailed amount, the customer is not required to plan equipment investment in energy-saving measures and collection thereof. Introduction of the energy-saving measures is thus made easier.