PURPOSE:To always set an optimally balanced impedance by computing the differential signal between a signal at one terminal of a subscriber line and the signal at a junction between a balanced impedance circuit and a terminal resistance, and generating a control voltage based on an amplitude display signal from a digital signal processing circuit. CONSTITUTION:When a positive and negative alternating signal is inputted to a transmission edge 10 as a training signal, the signals is inputted to a subtracter 6, converted into a digital signal by an A/D converter, inputted to a digital signal processing circuit 8, the control voltage is generated based on an amplitude display signal from the digital signal processing circuit 8, and outputted to a balanced impedance circuit 5. In such a case, by holding and outputting the controlled voltage generated in a controlled voltage generating circuit 9 at the time of training, even in a normal operating state, a balanced impedance Zb is differentiated from a value set at the time of training, and a near-end echo is suppressed. Thus even when the conditions of the subscriber line are changed, the optimally balanced impedance can be always set conforming to the respective conditions.