8. The speech dialogue system of claim 7, wherein the speech segment detection means uses detection thresholds for determining the speech segment which vary according to a power level of the synthetic speech response to be cancelled at the synthetic speech response cancellation means.
7. The speech dialogue system of claim 1, further comprising speech segment detection means for detecting a speech segment in the input signals, wherein the speech recognition means recognize the speech input from the input signals only at the speech segment detected by the speech segment detection means.