A power generation amount of a power generator disposed on a vehicle is appropriately controlled by ordering the power generator a required power generation amount so as to control the power generator, driving a drive motor configured to drive a driving wheel of the vehicle using at least part of electric power generated by the power generator according to the required power generation amount, storing at least part of surplus power left in the electric power generated by the power generator in a storage device, detecting a slip of the driving wheel, and, executing reduction processing of a power generation amount for further reducing a required power generation amount that reflects a reduction amount of the electric power for driving the drive motor due to the slip of the driving wheel, if the detected extent of the slip is larger than a predetermined threshold.