A digital communication system includes a transmitter and a receiver and communicates on telephone line. Receipt gain of the digital communication system is controlled in accordance with the following. Initialization signals generated at the transmitter and transferred through the hybrid circuit on the telephone line are received for a predetermined time period. An average magnitude value of the initialization signal received during the time period is compared with a reference magnitude value. Receipt gain is controlled according to the difference between the average magnitude value of the receipt signal and a reference value. In this manner, when the system performance is changed according to permissible tolerance of the analog discrete components used in the ADSL system, gain of the gain amplifier is automatically controlled. Thus, the ADSL system can operate with optimal performance under given conditions.