To reduce the running cost of a motor by simplifying the constitution of a driving device and reducing the size of the device and utilizing regenerated power for driving the motor by storing the power.

In a method for driving motor, DC power 18 converted from three-phase AC power 4 by means of a power converter 17 is fed in parallel to the inverter circuits 10 and 10' of three-phase AC motors 2 and 3, after the voltage fluctuation of the power 18 is absorbed by smoothing the voltage by means of smoothing capacitors 13 respectively installed to the inverter circuits 10 and 10', transistor blocks 11 for three-phase output feed the power 18 to the motors 2 and 3 after converting the power 18 into three-phase alternating currents. The regenerated power to the power 18 is used for charging a battery 27. When the regenerated power exceeds a prescribed value, the power is returned to the three-phase AC power 4 side after converting the power into a three-phase alternating current. In addition, when the regenerated power abruptly increases, the power is dispersed to and temporarily stored in the capacitors 13 and, when the power gradually increases, the power is used for charging the battery 27.