A data transmission system including a plurality of terminal devices arranged in a communication network and configured to transmit or receive content data. At least one terminal devices configured to receive content data transmitted from another terminal device, among the plurality of terminal devices, includes a reception priority management unit configured to manage priority of two or more content data addressed to the own terminal device, and a data reception control unit configured to, based on an output time interval of output signals corresponding to priority data whose priority managed by the reception priority management unit is high among two or more content data being received, request a transmission source configured to transmit content data having priority lower than the priority data, to perform control to stop transmitting the content data.