PURPOSE: To exclude a useless idle time by adopting the constitution such that the reception and transmission operations of a data transmission/reception means are controlled independently separately and a reception address generating means and a transmission address generating means are provided individually, and they are acted independently.

CONSTITUTION: The data transmission/reception means 6A1, 6A2 are constituted such that the receiving and transmitting operations are made controllable independently, and each data transmission/reception means is provided with separate address generating means assigned respectively thereto as the reception address generating means 5a and the transmission address generating means 5b, which are acted independently. A transmission address signal and a reception address signal are generated entirely independently while being synchronously with a frame synchronizing signal and the data transmission reception means receiving the signals control the operation of the transmission/reception entirely independently. Thus, a useless idle time between the transmission data and the reception data between the data transmission/reception means is excluded to the utmost, thereby decreasing the occupied time of the transmission line.