An object is to enable wireless communication between a portable terminal and on-board devices, and enable wireless connection to a train composition to be subjected to maintenance even in the presence of a plurality of train compositions. A control transmission device is mounted on a train and includes: a port connectable by wire to a maintenance communication device that is an external terminal; a train composition number notification unit that provides notification of a train composition number of the train; and a wireless network ID reception unit that receives a wireless network ID for constructing a wireless network. The wireless network ID received by the wireless network ID reception unit is generated based on the train composition number provided by the train composition number notification unit.