POWER SUPPLY DEVICE, AUTOMATIC STEERING VEHICLE, AND POWER SUPPLY METHOD

This power supply device is provided with: a primary power supply system for supplying power to a motor for rotary-driving a running wheel; a voltage converter unit for converting voltage by being supplied with a part of the power from the primary power supply system; a secondary power supply system for supplying electric power converted by the voltage converter unit to a steering device; and a primary backup power supply for supplying power to the voltage converter unit. The primary backup power supply makes it possible to supply the power to the voltage converter unit when the voltage of the power detected by a VD of the primary power supply system becomes smaller than a predetermined value.