Provided is a network that is constituted in a train formation; communication relay devices; terminal devices; and a position-information distribution device. The communication relay devices rewrite position information from the position-information distribution device to vehicle information indicating positions of vehicles that are provided with the communication relay devices and transfer rewritten information. The terminal devices include an IP-address correspondence table in which IP addresses that are set so as not to overlap with each other for respective types of the terminal devices and are to be used while corresponding to the vehicle information and connection destination information of the terminal devices correspond to each other. IP addresses to be allocated to the terminal devices are decided on the basis of the correspondence table and the vehicle information from the communication relay devices.