PURPOSE: To switch a communication procedure from a V.25bis line exchange procedure to a B-channel packet procedure without registering/setting a terminal adapter.

CONSTITUTION: When a regular transmission command based on the regulation of V.25bis of ITU-T advice is received from a data terminal equipment (DTE), data communication based on the line exchange procedure is set through a DTE interface 21, a line exchange control part 22 and a call control part 23. When a prescribed parameter is added to the transmission command, a B- channel packet control part 24 is connected to the data terminal equipment, and data communication based on the B-channel packet procedure is set through the B-channel packet control part 224 and the call control part 23.