To provide a current differential protective relay system which contributes to stable power supply by only disconnecting a defective system by preventing another sound systems from being affected by a system in which a failure occurs by only breaking the defective system, when the systems are separated from each other through a dividing circuit breaker and, at the same time, by separating the defective system by turning off the circuit breaker when the failure occurs, while the circuit is turned on.

A protective section changing circuit 5 is provided in an idle terminal discriminating circuit. The circuit 5 causes substations C and B which are farther than a dividing circuit breaker, when viewed from a substation, A to send idle signals 16C and 16D to other substations, when a dividing circuit breaker 'OFF' signal is inputted and the other substations which receives the 'OFF' signal forcibly set sent current data to zero by discriminating that the substations C and D are in idling states. Therefore, the substations which receive the 'OFF' signal is not affected by accidents which happen at locations farther than the dividing circuit breaker.