Provided are: a submarine cable system with which it is possible, with a simple configuration, to acquire the state of each of a plurality of high-voltage relays in a branching device; the branching device; and a state response method therefor. The branching device comprises: a plurality of interlocking relays respectively corresponding to a plurality of high-voltage relays for switching feeding paths; a drive unit which supplies drive electric currents supplied to the plurality of high-voltage relays to the plurality of corresponding interlocking relays, respectively; a state detection unit which detects operation states of the plurality of interlocking relays as the operation states of the plurality of high-voltage relays; and a response unit which, on the basis of the result of detection of the operation states of the plurality of interlocking relays, transmits the operation states of the plurality of high-voltage relays.