A vehicle-mounted antenna system includes a combined antenna apparatus that has a GPS antenna and a short-range wireless communication antenna. The GPS antenna is directional in a vertical direction and the short-range wireless communication antenna is directional in a horizontal direction. The combined antenna apparatus is mounted below an instrument panel of the vehicle by a mounting bracket in such a manner that the short-range wireless communication antenna is directional in the horizontal direction toward an interior of a vehicle. This approach ensures adequate performance of the short-range wireless communication antenna and standardizes a manner in which the short-range wireless communication antenna is mounted to the vehicle.