PURPOSE: To eliminate the need for the response with an incoming call and to eliminate the need for charging of a telephone tariff by controlling an external device according to an incoming sub-address in the ISDN telephone set.

CONSTITUTION: An external device control memory section 8 storing an ID code and an external device control code corresponding to each ID code is provided in a data memory section of a main device 2. A central processing unit 4 reads incoming call sub-address information from setup information sent from an ISDN line and matches a cell painter to a head cell of the external device control memory section 8 and compares the ID code stored in a cell designated by a cell pointer with the incoming sub-address information. When the ID code and the incoming sub-address information are coincident, the external device control code stored in the cell is read and the relevant external device is controlled.