PURPOSE: To attain the communication for both an exchange line and a communication equipment for an exchange line by means of a general-purpose software.

CONSTITUTION: A telephone number verification section 16-1 in a control section 16 receiving a dial command from a DTE compares a telephone number in the dial command with a telephone number registered in a telephone number registration area 17. Telephone numbers corresponding to exchange line communication equipments are registered in advance in the telephone number registration area 17 and when the telephone numbers are coincident with each other as the result of comparison by the telephone number verification section 16-1, a changeover switch 13 is thrown to the position of an external communication equipment interface section 15 and the control section 16 controls a MODEM section 12 after the changeover to conduct communication to the exchange line communication equipment. When the telephone numbers are dissident, the changeover switch 13 is thrown to the position of an NCU section 14 and the communication with the exchange line is conducted via the NCU section 14.