To provide a current differential protective relay device which allows prevention of erroneous detection of monitoring failures in a substation at one end of a transmission line, and is constituted so that a current transformer is positioned closer to the other end than to a ground isolator is.

A condition obtained by combining the condition of this-end line isolator closed with a condition of this-end circuit breaker closed via an AND element 11 is taken as a failure detection this-end condition 15. Similarly, a condition obtained by combining a condition of other-end line isolator closed acquired from the other end by transmission with the conditions of other-end circuit breaker closed acquired from the other end by transmission via an AND element 12 is set as a failure detection other-end condition 16. An AND element 13 is set by combining the failure detection this-end condition 15 with the failure detection other-end condition 16, and the result of combination is taken as failure detection condition 17. When an AND condition 14 of the failure detection condition 17 and a differential current Id failure of differential current monitoring holds, a failure is detected. As a result, when any one of a substation A circuit breaker, a substation A line isolator, a substation B circuit breaker, or a substation B line isolator is open, failure detection is locked so that even if an induced current is produced, unnecessary detection can be avoided.