An in-vehicle power supply device according to the present disclosure includes an input terminal, a charge-discharge circuit connected to the input terminal, a first output terminal connected to the charge-discharge circuit via a first switch unit and a first cut-off unit, a second output terminal connected to the charge-discharge circuit via a second switch unit and a second cut-off unit, and a controller connected to the input terminal, the first output terminal, and the second output terminal. The controller controls the charge-discharge circuit, the first switch unit, the first cut-off unit, the second switch unit, and the second cut-off unit. When the controller detects that a voltage of the first output terminal becomes lower than the first load threshold voltage, the first cut-off unit changes from a connected state to a cut-off state. After a lapse of a first predetermined period following a time at which the controller detects that the voltage of the first output terminal is lower than the first load threshold voltage, the second switch unit switches from a state of higher-resistance conduction to a state of lower-resistance conduction in which a resistance level is lower than the resistance level in the state of higher-resistance conduction.