The hybrid car power supply apparatus is provided with a battery system 1 having a driving battery 2 to run an electric motor 3 to drive the vehicle, an inverter 4 to drive the electric motor 3 with the driving battery 2, and an automotive battery 5. The battery system 1 houses a charging circuit 7 to charge the driving battery 2 with the automotive battery 5. The charging circuit 7 charges the driving battery 2 with the automotive battery 5 when remaining driving battery 2 capacity becomes low. The charged driving battery 2 runs the electric motor 3 to start the engine 8.