A method of disconnecting a secondary battery which disconnects the secondary battery from an electric power supply path in an electric power supply system performs shutting off a flow of a current to a secondary battery side through a converter after it is detected that there is an abnormality in the secondary battery, and when it is determined that the voltage of the power storage unit is equal to or less than the voltage of the secondary battery by the predetermined value, maintaining a connection of the secondary battery to the electric power supply path and when it is determined that the voltage of the power storage unit is greater than the voltage of the secondary battery by the predetermined value, operating a relay to disconnect the secondary battery from the electric power supply path.