To minimize the amount of calculation for changing an operation schedule even when there is an increase in the number of sites. A management computer calculates a first total schedule value, which is the total of the schedule values for each of the sites within a first time frame. If the first total schedule value exceeds a first target value set in advance, the management computer: calculates a first excess amount of the first total schedule value in relation to the first target value; selects, as a first site, a site subjected to a change in a demand schedule from a group of candidate sites satisfying a candidate criterion set in advance from among a plurality of the sites, the selection being performed on the basis of information on the facility characteristics for each of the sites; changes a first demand schedule of the first site in the first time frame; and transmits the changed first demand schedule to a control device of the first site.