Back-up power source device and back-up system

A back-up power source device comprising a shift-by-wire device that switches a shift range of an automatic transmission using driving force from a motor and a back-up power source that supplies power to the shift-by-wire device, the back-up power source device supplying power from the back-up power source to a shift control unit included in the shift-by-wire device in the event of a battery failure in which the supply of power from a battery is lost, the back-up power source device further comprising:

• a failure detection unit that detects the battery failure;
• a monitor unit that, when the battery failure has been detected by the failure detection unit, monitors a user's operation of a switch instructing unit that instructs the shift range to be switched to a parking range, and generates an instruction signal in response to the operation of the switch instructing unit;
• and
• a back-up control unit,
• wherein the back-up control unit executes:
• a battery failure determination process of determining whether or not the battery failure has been detected by the failure detection unit;
• when it is determined that the battery failure has been detected in the battery failure determination process, a switching instruction determination process of determining, on the basis of the instruction signal generated by the monitor unit, whether or not the instruction to switch has been made;
• and
• when it is determined that the instruction to switch has been made in the switching instruction determination process, a shifting instruction process of starting power supply from the back-up power source to the shift control unit and instructing the shift control unit to shift to the parking range.