PURPOSE: To make an operating clock independent by distributing voice signals added by each loop to each terminal equipment while being transferred sequentially to a distribution channel so as to prevent propagation of an error of one loop to other loop.

CONSTITUTION: Voice data added by an addition channel 5 are sequentially transferred to an change channel 10 and a distribution channel 6 sequentially by a channel exchange register 12 in each of loops #1, #2, the loops are terminated by the exchange register 12 to allow each of the loops to form an independent logic loop. When an error takes place in the loop #2, for example, a data control section of the loop #1 in the loop link master station side cancels voice data on an exchange channel 10 of the loop #2 to use an adder 11a to add the data to voice data on the exchange channel 10 of the loop #1. Thus, the effect of a fault of the loop #2 is not given onto the loop #1 and conference speech in the loop #2 is maintained.