To prevent a shortage of power of a customer who utilizes a private electric generator, without practically purchasing power from an electric power company.

Two groups A, B, which comprise respectively a plurality of private electric generators composed of power-generating installations which also supply heat together, are provided. When generated electric energy of each installation 1 is insufficient for electric energy of load power, an overall supervising apparatus 20 connected through an individual monitor 10 attached to each installation 1, attempts to solve the power shortage by self consignment of power in each group A, B. If the power shortage is not solved by the self consignment of power, the overall apparatus 20 attempts to solve the power shortage, by performing retail consignment between the different groups A, B. If the power shortage is not solved even by retail consignment, the overall apparatus 20 gives power-generating installations instructions to consign the insufficient component of power.