AUXILIARY POWER SOURCE DEVICE

An auxiliary power source device (40) includes a main power source-side path (LI), an auxiliary power source-side path (L2), a power source control circuit (70), an analog determination circuit (100) that is provided separately from the power source control circuit (70), and a power source switching circuit (110). The power source control circuit (70) controls switching between a conduction state and an interruption state on the main power source-side path (LI) and the auxiliary power source-side path (L2). The analog determination circuit (100) determines an occurrence of abnormality in the main power source (50) and generates a switching signal when the occurrence of the abnormality in the main power source (50) is determined. The power source switching circuit (110) switchs a power source for supplying power to a power supply target, from the main power source (50) to the auxiliary power source (60).