PURPOSE: To eliminate the need for new installation of a communication line or building of a local area network by connecting plural terminal equipments and a hot computer to an indoor distribution wire via a spectrum expansion MODEM and an attenuation means.

CONSTITUTION: When the operator of a message input terminal equipment 15-2 operates a keyboard and inputs a message data, an SS MODEM interface 12-5 modulates the message data to obtain a signal of spread spectrum. The signal is supplied to a lighting line 10 via an SS MODEM interface 12-4 and an attenuator 11-2, and fed to an attenuator 11-1 through the lighting line 10. Moreover, the signal is received from the SS MODEM interface 12-4 through SS MODEM interfaces 12-1-12-3. Since the existing indoor distribution line is used as the transmission line in this way, it is not required to install a new transmission line or a local area network.