put unit on the transmitter side of the ADSL.Lite modem 6 a, which is the output serial/parallel buffer 91 or the DA converter analog processing 92, for example, in such a manner as to remove the band of about 15 to 20 Hz constituting the ring tone signal frequency. [0064] By doing so, as shown in FIG. 5(c), even when the data communication is conducted using the audio band of 4 kHz in the on-hook