A power interrupting device has: an output terminal connected to a load; interruption circuits connected in parallel between a power source and the output terminal; and a control device controlling each interruption circuit. Each interruption circuit has: a switch element connected between the power source and an intermediate node, and ON/OFF controlled by an interruption signal output from the control device; and a rectifier connected such that a forward direction thereof is from the intermediate node to the output terminal. The control device sets the interruption circuits as a diagnosis target circuit in turn. The control device sets the interruption signal output to each interruption circuit such that the switch element of the diagnosis target circuit is OFF. Moreover, the control device determines, based on a voltage of the intermediate node of the diagnosis target circuit, whether an abnormality occurs in the diagnosis target circuit.