Abstract: A key telephone apparatus includes a main device which is connected to a telephone network line and a plurality of extension telephones connected to the main device. When the line dialed from the extension telephone is busy, the busy tone signal transmitted to the extension telephone is detected by a tone detection circuit provided in the extension telephone. In response to the detection of the busy tone signal, a controller provided in the extension telephone produces a redial command which is applied to a controller provided in the main device. Thus, a controller redials for the same line after a predetermined time interval. If the line is still busy as detected by the tone detection circuit in the extension telephone, the controller provided in the extension telephone sends the redial command to the controller provided in the main device which repeats the redialing after the predetermined interval.