In-vehicle power source apparatus

A vehicle power source apparatus is provided with a driving battery (5) mounted in a vehicle, an auxiliary apparatus battery (11) that supplies electric power to an auxiliary apparatus (10) of the vehicle, a DC power conversion unit (1) that supplies electric power from the driving battery (5) to the auxiliary apparatus battery (11), a control unit (2) that controls the DC power conversion unit (1), a driving battery harness (7) that connects the driving battery (5) with the DC power conversion unit (1) and is protected by a shield (6), an auxiliary apparatus battery negative-side harness (13) that connects the DC power conversion unit (1) with the negative side of the auxiliary apparatus battery (11), and a voltage sensor (3) that detects a connection abnormality in the auxiliary apparatus battery negative-side harness (13).