PURPOSE: To drive a rotating machine and, at the same time charge one of the two batteries which is not charged fully by a current from a generator coupled with the rotating machine, by operating a hydraulic motor by a current of the other one of the two batteries which is charged fully.

CONSTITUTION: Two batteries are prepared, one of which is charged fully and the other is charged to 50W60%. When a switch is turned on to operate a hydraulic motor 16, an oil pump 14 coupled directly to it is operated and oil in an oil tank 12 flows via an oil strainer 13, a high pressure pipe 15 and a change-over valve 17 to a low pressure pipe 5 and rotates a rotating machine 2, therefore, a wheel disc 8 is rotated. And by a current supplied from a generator coupled with the disc passing through a changeover switch for charging and current supplying, another battery not charged fully is charged.