PURPOSE: To save a TDM time division multiplexer at the center, by providing a TDM time division multiplexing function at the center in a communication controller intermediating a data communication between data processors at the center and a terminal device.

CONSTITUTION: A center-side communication controller having a host computer is provided with a parallel serial converter 2 multiplexing a signal from a plurality of terminal interfaces 1 and transmitting the signal to an MODEM 7, a timing formation circuit 3, and also a serial parallel converter 4 distributing the signals from the MODEM 7 to the terminal interfaces 1, and a timing formation circuit 5. The MODEM 7 performs communication with an MODEM at terminals via a line (not shown). In the communication controller, one of the plurality of terminal interfaces 1 controls and monitors the MODEM 7 of high speed lines as the representative and performs signal multiplexing of all the terminal interfaces and transmits signals, based on the synchronizing timing of the high speed line.