In an apparatus, a first detecting unit detects the number of revolutions of a power generator, a second detecting unit detects an output voltage of the power generator, and a third detecting unit detects an output current of the power generator. A torque calculating unit calculates power generation torque based on the detected number of revolutions of the power generator, the detected output voltage, and the detected output current using relationship information. The relationship information represents a relationship between the power generation torque and each of the number of revolutions of the power generator, the output voltage, and the output current.