To solve the problem of maintainability which arises, especially in a system requiring a large number of backup capacitors, since voltage is kept by the use of backup capacitors up to now to enable continuous system operation, on the occasion of an instantaneous stop in a driving system provided with a small-inertia load, and the capacitors are consumable parts.

This system is provided with two motor-driving systems 30, 31 of different driving voltages, and a common AC power source 15 for supplying power to both driving systems, and supplies power to one driving system 31 through a transformer 13. An inverter unit 20 for instantaneous-stop-time exclusive use is interposed between both driving systems. On the occasion of an instantaneous stop, regenerative power from a motor 17 belonging to the other driving system 30 is supplied to the one driving system 31 through the inverter unit exclusively used for instantaneous-stop and the transformer.