PURPOSE: To make it possible to parallel off a distributed power device from a power distribution system and to prevent the independent operation of the distributed power device by opening a switch for performing the parallel off of the distributed power device connected to a distribution line having a distribution-line leading-out circuit-breaker, in case that the circuit-breaker should sperate.

CONSTITUTION: In case that a central arithmetic processor 18 should recognize the operation of a distribution line leading-out circuit-breaker 11 in a distributing substation 10, a switch S6 for performing the parallel-off of a distributed power device connected to a distribution line 14 provided with the circuit-breaker 11 is opened. Consequently, it becomes possible to perform the parallel-off of a distributed power device G from a power distribution system in a power distribution system being a monitoring and controlling object, in an operation of the distribution-line leading-out circuit-breaker II put there, and it becomes possible to prevent the distributed power device G from falling into independent operation by performing control from the side of the central arithmetic processor 18.