PURPOSE: To always use the capacity of a communication channel to a maximum and to shorten the whole communication time by transmitting information desired to transmit to a communication opponent by an opponent by using a time until an operator on a transmitter side performs input, etc.

CONSTITUTION: When the transmitter 1 side sets a communication path by main communication between a receiver 2 side on modem control parts 2aa, 2ba at two specific points, multiplex data communication reservation information or default communication reservation information based on a prescribed code is registered on a prescribed area on the reception 2 side with the destination identifier of a transmitter 1. When the transmitter 1 side sets the next communication path and the receiver 2 side recognizes the fact that such reservation information is registered, the free time of the communication channel 4 by the main communication is detected, and registered information is transferred to communication equipment (transmitter 1) specified by the destination identifier by background communication separated from the main communication.