The purpose of the present invention is to reduce the acquisition time of location information without installing new equipment. Provided is a location detection system which is disposed in vehicles and comprises a vehicle-mounted device (1) provided in a vehicle and also provided in another vehicle, each of said vehicle-mounted devices (1) being provided with a location detection unit (3) for detecting the location of the respective host vehicle, a communication unit (5) for carrying out communication, and a CPU unit (2) for controlling the location detection unit (3) and the communication unit (5). The location detection system is characterized in that each vehicle-mounted device (1) is further provided with a global positioning system (GPS) tracking information processing unit (4) for obtaining GPS tracking information of each vehicle, the communication unit (5) of one vehicle broadcasts a GPS tracking information request, the communication unit (5) of the other vehicle transmits the GPS tracking informati
