Contactor failure determining method and contactor failure determining device

A contactor failure determining device comprising:

• a contactor control unit that outputs a control signal for switching a positive-side contactor provided between a positive electrode of the multi-cell battery and a positive electrode of a load to which the multi-cell battery supplies electric power to an open state at the end of supply of high-voltage power from a state in which a control signal for controlling the positive-side contactor and a negative-side contactor provided between a negative electrode of the multi-cell battery and a negative electrode of the load to a closed state and a precharge contactor provided between the multi-cell battery and the load to an open state is output;
• and
• a determination unit that determines a presence of fixing of the precharge contactor based on a degree of voltage drop of a voltage applied to the load after the control signal for switching the positive-side contactor to the open state is output.