A maximum current Imax is calculated on the basis of an open-circuit voltage Voc, a lower limit voltage Vcapmin, and an internal resistance Rcap of a capacitor and a first maximum output Wcouttmp1 is calculated on the basis of the maximum current Imax and the lower limit voltage Vcapmin. A second maximum output Wcouttmp2 is calculated on the basis of the open-circuit voltage Voc and an open-circuit lower limit voltage Vocmin. A third maximum output Wcouttmp3 is calculated on the basis of a capacitor voltage Vcap and the lower limit voltage Vcapmin. A smallest value among the calculated three maximum outputs is set as an execution maximum output Wcout of the capacitor. A motor is controlled to be driven in a range of this execution maximum output Wcout.