An automobile power supply device is provided with a first relay interposed between a first battery and a load group; a second relay interposed between second battery and the load group; a hood switch that detects the opening of a hood of an engine room and outputs a detection signal dt1; a luggage switch that detects the opening of a hood of a luggage room and outputs a detection signal dt2; and a power supply control unit that brings the first relay into a non-conductive state based on the detection signal output by the hood switch, and brings the second relay into a non-conductive state based on the detection signal output by the luggage switch.