Abstract: A system for automatically compensating the transmitting (outgoing) signal level by detecting the receiving (incoming) signal level received from a communication channel to MODEM. Said system includes a gain controller for controlling the output gain of the analog signal received from analog signal input terminal in accordance with gain control data, hybrid means for amplifying the output of said gain controller, providing the amplified signal to transmit to a telephone line, and amplifying the analog signal received from the telephone line, receiving level sensing means for providing a plurality of receiving information data, said receiving information data teaching the level of the received signal, and a microprocessor unit for outputting the gain control data to said gain controller in response to the receiving information data and initial gain control data stored therein.