In order to effectively supply and demand electric power between an electric power supplier and a node or a group of nodes individually having an electric power generator, the present invention provides an electric power supply and demand management system capable of obtaining the difference between the total of electric power supplied from the electric power supplier to the node or group and the total of electric power consumed by the electric power loads of the node or group and capable of transmitting information for increasing/decreasing the amount of electric power supply so that the difference becomes smaller to the electric power supplier.