In data communication between a terminal equipment connected to a first network and a second network and a server terminal equipment via an interconnecting installation, there are provided a first communication controller in which data communication control is performed on the terminal equipment via the first network by a message group for functions of data transfer, transmission acknowledgment, flow control, and the like, and a second communication controller in which the data communication control is performed on the interconnecting installation with the terminal equipment via the first network by the message group, and the data communication control is performed with TCP module of the server terminal equipment according to TCP. By this, data communication efficiency is enhanced in a communication environment for communicating a communication terminal equipment on a cable network through a radio line or another access link.