To prevent reduction in the capacitance of, and shortening of the life of, an uninterruptible power supply, by stopping power supply from the backup power supply system for the uninterruptible power supply if an ordinary power supply out of control fails when a driving device is in standby state and is not restored after a specified time has passed.

If a power failure further occurs during standby, the backup power supply for a battery 41 is outputted, and a standby power supply is backed up. At the same time, a timer circuit 44 starts counting, and whether the power failure is recovered during time counting is judged based on whether commercial power supply is alive. When the power failure is judged to have been recovered before the timer circuit 44 expires, it is judged as a short-time power failure, and the output of the battery 41 is interrupted and processing is resumed. When the timer circuit 44 expires, that is judged as a long-time power failure, and the output of the battery 41 is interrupted until power recovery. When it is judged through monitoring of commercial power supply that power supply has been recovered, the interruption of the output of the battery 41 is canceled.