To provide a vehicle controller which can control a dual voltage compatible vehicle so that the engine start can be secured even when the voltage drops in one of the batteries and this battery is protected from complete discharging.

In a vehicle controller, a voltage monitor 9 monitors the output voltages of a 36-V battery and a 12-V battery, and if it detects that either one of the voltages drops, the voltage of the other battery is boosted up or stepped down by a DC-DC converted and supplied to it. Thus, in either case, the control circuit 7 and the first drive circuit 61 can be operated to start the engine. When the engine starts, the alternator 2 generates power and charges the battery whose output voltage is low.