PURPOSE: To materialize exact overdischarge prevention of a nonaqueous secondary battery using carbon material capable of doping it with lithium ions as negative electrode active materials or dedoping the lithium ions therefrom.

CONSTITUTION: The overdischarge of a nonaqueous secondary battery B using carbon material, capable of doping it with lithium ions as negative electrode active materials or dedoping the lithium ions therefrom, is prevented at the time of discharging. This is equipped with a voltage detecting circuit 2, which detects the terminal voltage E of the nonaqueous secondary battery B having dropped to a set voltage Ee of approximately 35 to 65% of full charge terminal voltage, and a power supply stop circuit 3, which stops the power supply from the nonaqueous secondary battery B to a part M supplied with power upon function of the voltage detecting circuit 2.