A charge accumulating circuit accumulates regeneration power. The charge accumulating circuit includes a DC bus line which is connected to a smoothing capacitor, a charge accumulating capacitor with an internal resistance, and a converter which connects the DC bus line and the charge accumulating capacitor to each other, and performs a charge/discharge operation. The control device changes the OFF state of the first switch to the ON state when the start key is turned on, measures a physical quantity involved with a discharge characteristic of the charge accumulating capacitor, and calculates at least one of the internal resistance and a capacitance of the charge accumulating capacitor on the basis of a measurement result.