PURPOSE: To eliminate the state of excessive addition of a PCM signal even in a form of communication connecting to a ring by providing a digital subtraction means cancelling a PCM input signal component from its own station from a PCM signal inputted from two connection sections with respect to 1st and 2nd directions except the direction of its own station to a pre-stage of a branch insertion means.

CONSTITUTION: A PCM input signal S11 from a direction A is inputted to a synchronization detection circuit 5 via a reception section 1, the synchronization detection circuit 5 detects a synchronous pattern added to the PCM input signal S11 to recognize the pattern of the PCN input signal S11 and outputs the PCM input signal S11 to a subtraction circuit 12. On the other hand, a PCM input signal S51 from its own station is corrected for delay by a delay circuit 10 by a delay stored in advance in a delay storage memory 9 to match the phase of the PCM signal from the synchronization detection circuit 5. The subtraction circuit 12 subtracts its own PCM input signal s51 subject to delay and correction by a subtraction circuit 10 at a pre-stage from the PCM signal in the synchronization detection circuit 5 digitally. Thus, the state of excess addition of the PCM signal is avoided.