<p>The clock discrepancy between the speaker side (receiving side) and microphone side (transmitting side) of a bilateral telephone conversation capable apparatus is detected to shift, based on the detected discrepancy, the frequency of a first frequency signal (speaker signal (reference signal)) or that of a second frequency signal (microphone signal) in a frequency range, whereby the affection caused by the clock discrepancy can be simply corrected without increasing the process amount, thereby effectively suppressing the echo.</p>
