PURPOSE: To execute training to any circuit at an optimum speed, by constituting so that a receiving device initialized by the first training signal is corrected by the second training signal.

CONSTITUTION: In case when a data is transmitted to a center device CPU from a terminal station device DTE #1, the DTE #1 raises a transmission request signal line in an interface line (if) connected to a station MODEM #1. In response to it, the SMD #1 supplies a training signal to a circuit l. When sending out the training signal by the SMD #1 ends, the DTE #1 transmits a data, and the SMD #1 supplies this transmitting data to the circuit l. When the main MODEM MMD receives this training signal and the data signal, it executes each adjustment by use of this training signal. Subsequently, the SMD #1 generates the second training signal having duration corresponding to a characteristic of the circuit. The MMD utilizes this signal as training information in its own device, and demodulates a data signal following said signal.