A vehicle power-supply control device has a battery charger that converts an externally-supplied AC voltage into a DC voltage used to charge a vehicle high-voltage battery, a low-voltage power generator that converts the DC voltage output from the battery charger into a DC voltage used to drive a vehicle auxiliary machine, and a controller that controls the battery charger and the low-voltage power generator. The battery charger includes a power factor correction circuit that corrects a power factor of the AC voltage and a first DC/DC converter that generates a predetermined DC voltage based on an output of the power factor correction circuit. The low-voltage power generator includes a second DC/DC converter that steps down the DC voltage output from the battery charger and a synchronous rectifier that rectifies an output of the second DC/DC converter in synchronization with a switching operation of the second DC/DC converter.