A battery management system (BMS) is provided, which includes: an on-off switch provided in a current path connecting an assembled battery and electrical equipment; a controller that switches the on-off switch to an off-state when an abnormality in the assembled battery is expected; and a bypass route connected in parallel with the on-off switch and having at least one of a parasitic diode that allows current to flow only in a direction of charging the assembled battery and a parasitic diode that allows current to flow only in a direction of discharging the assembled battery. A second excitation coil is connected in series with the parasitic diode and the parasitic diode 50B in the bypass route, the second excitation coil switching the on-off switch to an on-state with magnetic flux by flow of current with a predetermined current value.