A control device has a unit for determining a controlled phase of a controlled voltage outputted from an inverter to a generator according to a difference between a target torque and an estimated torque of the generator, a unit for calculating an instructed vector norm of the controlled voltage from the target torque, an electrical angular speed of the generator and parameters indicating characteristics of the generator, a unit for correcting the instructed norm to an adjusted vector norm such that a phase of current flowing through the generator in response to the controlled voltage set at the controlled phase and the adjusted norm is controlled to a phase of an instructed current determined from the target torque, and a unit for controlling the generator by controlling the inverter to output the controlled voltage set at the controlled phase and the adjusted norm to the generator.