A vehicle fault determination device includes a relay, a vehicle configuration circuit, and a control section. The relay is connected to a power source. The vehicle configuration circuit is supplied with power from the power source via the relay. The control section determines whether the relay is faulty while controlling the relay and the vehicle configuration circuit. The control section includes first and second ports. The first port outputs a control signal to a coil portion of the relay. The second port is connected to a contact portion of the relay via the vehicle configuration circuit. The second port serves as an input port when the fault determination is made and as an operation port when the vehicle configuration circuit is controlled. Thus, the number of parts is keep to a minimum to increase the number of dedicated ports for determining whether the relay is faulty.