A train communication system includes a communication relay device that is installed in each vehicle and a communication terminal device that is connected to the communication relay device. The communication relay device acquires vehicle information indicating an in-formation position of a vehicle in which the communication relay device is installed. The communication terminal device refers to a correspondence table that defines a correspondence relationship between vehicle information and communication identification information, and determines communication identification information to be provided to the communication terminal device, based on vehicle information obtained from the communication relay device.