PURPOSE: To keep the transmission quality of an entire network by abandoning cells according to the priority of data when any obstruct is generated at a repeater line.

CONSTITUTION: Each time the communication of a terminal 100 is finished, first ATM throughput inside a CPU 18 decided at the terminal 100 is corrected based on measured second ATM throughput. When connection with a repeater line 110 is enabled based on the first ATM throughput of the terminal 100, the second ATM throughput transmitted by the terminal 100 is measured by an HT (header transducing) part 11, a non-preferential identifier is applied to the cell of transmitting data by the HT 11 from excess over the previously decided first ATM throughput to reduction under the first ATM throughput and when the repeater line 110 is obstructed, the cell to which the non- preferential identifier is abandoned by an HT 13. Thus, the band of the repeater line 110 is allocated based on the result of communication without depending on the degree of exactness of the throughput to be declared.