Recently, various services using road-vehicle communications have been put to practical use, and information on the running history and performance data of the vehicle is uploaded to the roadside and expanded to services that use it in addition to the information delivery from the roadside to the vehicle. The "in-vehicle information terminal" interfaces with the car navigation system and the electrical equipment control system after it meets intelligent transportation system (ITS) on-board unit Dedicated Short Range Communication (DSRC) standards. This terminal also mounts functions for observing the state of the vehicle and controlling the vehicle remotely from the roadside by DSRC. In this project, the protocol that connects the roadside with the in-vehicle network was developed. Additionally the in-vehicle information terminal and the roadside system were developed, which achieved reading and writing of vehicle data via DSRC and Controller Area Network (CAN). Moreover, "car security" was created as a DSRC application service, an experimental system was developed, and the usefulness of the service was evaluated.