PURPOSE: To attain presence of circuits corresponding to both terminal equipments in mixture and to suppress increase in the number of buffers by arranging alternately even number order and odd number order of two-channel and one-channel transmission circuits so as to connect any transmission circuit to terminal equipment circuits depending on the type.

CONSTITUTION: A two-channel transmission circuit 11 is provided respectively to even number output terminals #0, #2... and a one-channel transmission circuit 12 is provided respectively to odd number output terminals #1, #3... in a B- channel transmission section circuit 10. The same number of the circuits 11, 12 are arranged and the total number of the both corresponds to the number (n) of output terminals. When a terminal equipment is two channel type, outputs of the even number output terminals #0, #2... are connected to a line termination section connecting to the terminal. When a terminal equipment is of one-channel type, outputs of the odd number output terminals #1, #3... are connected to a line termination section connecting to the terminal. Thus, any of the two- channel and the one-channel terminals is connected to a B-channel transmission circuit 10.