A vehicle power source apparatus is provided with a driving battery mounted in a vehicle, an auxiliary apparatus battery that supplies electric power to an auxiliary apparatus of the vehicle, a DC power conversion unit that supplies electric power from the driving battery to the auxiliary apparatus battery, a control unit that controls the DC power conversion unit, a driving battery harness that connects the driving battery with the DC power conversion unit and is protected by a shield, an auxiliary apparatus battery negative-side harness that connects the DC power conversion unit with the negative side of the auxiliary apparatus battery, and a voltage sensor that detects a connection abnormality in the auxiliary apparatus battery negative-side harness.