To provide a means for extending the time for continuously using a low-voltage drive device.

When a system power supply is turned on, a control system device periodically measures battery voltage data of a main battery 1, and when a battery voltage drops to preset voltage data or below, the system power supply outputs a detection voltage shift signal to a voltage detector 2 for the system power supply from the control system device. When the detection voltage shift signal is input, the voltage detector 2 for the system power supply short-circuits a resistor 208 by switching an SW 209 to an on-state from an off-state. By this, the detection voltage of the main battery 1 is raised. When the battery voltage of the main battery 1 drops to the raised detection voltage or below, a comparator 204 shuts down a system other than the low-voltage device by switching an output signal of the voltage detector 2 to L from H.

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