PURPOSE: To accommodate lines with an excellent efficiency and high cost performance by utilizing the performance of a line control processor sufficiently to both a low speed and a high speed line.

CONSTITUTION: Line control processors 1,2 control independently respectively line adaptors 1a-1d and 2a-2d. A line expansion wiring board (not shown) is mounted in place of the line control processor 2, and a control signal group 1e of the line control processor 1 is connected also to the line adaptor groups 1a-1d and 2a-2d by using a line expansion relay signal line group of the line expansion wiring board, then the line adaptors able to be controlled by the line control processor 1 is expanded. Thus, the line control processors and the line adaptors of a required number are accommodated on the same board depending on the speed of a line to be accommodated.