To provide a cost-effective regenerative energy protecting circuit, with a chopper circuit applied thereto.

To prevent a secondary battery 2 from being overcharged due to the regenerative energy of an electric vehicle, a series circuit comprising a resistor 11 and a switching circuit 12 is connected across the battery 2, a VF converter 13 is connected between the battery 2 and the control terminal of the switching circuit 12, and a constant voltage circuit 14 is inserted in series between the VF converter 13 and the battery 2.