PURPOSE: To reduce the communication cost by switching a terminal-side modem from an in-use mode to a stand-by mode through remote operation from a center side without using any subscriber line.

CONSTITUTION: A center-side electronic computer 1 is connected to a terminal equipment 6 through a modem 2 for data communication, a communication channel 3, an in-use modem 5A or stand-by modem 5B, and a switching device 4. Here, the terminal-side modems 5A and 5B are switched from the in-use mode to the stand-by state through the remote operation from the center side without using any subscriber line so as to send a switching control signal for switching the terminal-side modems 5A and 5B to the terminal side through the data communication channel 3. Consequently, the terminal-side modems 5A and 5B are brought under remote switching control without any communication cost.