With regard to electric-power-supply control, there is provided an electric power supply control system for implementing load control used to be executed for each individual customer consuming electric power as coordinated control for all customers and for selecting an optimum electric-power supplier in case there are a plurality of electric-power suppliers supplying electric power to the customers. Disclosed is the electric power supply control system for purchasing electric power from a plurality of electric-power suppliers and distributing purchased electric power to any arbitrary number of customers, the system comprising: an electric-power-purchase determining apparatus for selecting some of the electric-power suppliers and determining amounts of electric power to be purchased from the selected electric-power suppliers in accordance with a predetermined rule; an electric-power storage apparatus for storing electric power; and a demand control apparatus for transmitting electric power obtained by synthesizing electric power determined by the electric-power-purchase determining apparatus with electric power generated or absorbed by the electric-power storage apparatus to the customers.