The present disclosure relates to a protective relay detecting disconnection in a circuit comprising a disconnection detection unit including a plurality of nodes connected to both ends of an output of a transformation unit, a reference voltage generation unit forming a reference voltage, and a plurality of resistors forming a voltage dividing resistor and connecting the plurality of nodes and the reference voltage generation unit; a sensing voltage generation unit applying a voltage for forming a predetermined voltage difference with respect to the reference voltage; and a disconnection determination unit connected to a first node, in which the magnitude of a voltage signal applied by the voltage dividing resistor varies depending on whether at least one of the transformation unit and the circuit connected to the transformation unit is disconnected, and detecting whether at least one of the transformation unit and the circuit connected to the transformation unit is disconnected.