A device for controlling vehicle power generation that controls duty cycle of an excitation winding in a vehicle power generator and controls an output voltage from the vehicle power generator to a predetermined value includes a power generation controlling circuit that, when the output voltage from the vehicle power generator is less than the predetermined value, gradually increases the value of a gradual excitation duty and gradually increases the excitation current, the gradual excitation duty being a limit value for increasing and decreasing an excitation drive duty intermittently controlling the electrification of the excitation winding, and in an opposite situation, gradually decreases a value of the excitation drive duty and gradually decreases the excitation current. The power generation controlling circuit changes the rate at which the value of the gradual excitation duty is decreased.