A roadside apparatus is connected to a roadside network and an in-vehicle apparatus which carries out wireless data transfer with the roadside apparatus, and it is equipped with a specifying unit for specifying an in-vehicle apparatus by associating an IP address which was assigned with respect to each in-vehicle apparatus, and an in-vehicle apparatus identifier other than an IP address. By this configuration, between the roadside apparatus and the in-vehicle apparatus, enabled is data communication which utilized an IP series communication protocol for specifying an in-vehicle apparatus by use of an IP address which was assigned with respect to each in-vehicle apparatus, and a non-IP series communication protocol for specifying an in-vehicle apparatus by use of LID.