A control device for a motor-driven 4WD (four-wheel-drive) vehicle includes a 42v alternator (motor-generator) driven by an engine to generate three-phase AC power with 42 volts, a step-up and step-down inverter rectifying and stepping down three-phase AC power, generated by the 42v alternator, to DC power with 14 volts, and a 14V battery supplied with and charged with DC power with 14 volts outputted from the step-up and step-down inverter. A diode bridge circuit rectifies AC power with 42 volts, generated by the 42V alternator, to DC power by which a motor is rotationally driven to render the vehicle operative in 4WD drive mode.