The conventional speakerphone using the voice switch, when combined with the echo canceler, involves a problem that the threshold for switching the transmit/receive state of the voice switch cannot comply smoothly and stably with the performance variation of the echo canceler, thereby obstructing echo canceling in a manner that the voice switch cooperates with the echo canceler. The speakerphone of the invention estimates the performance variation of the adaptive filter by using the integrated value of a power of the receive signal or the transmit signal referred in the past when the adaptive filter learns, and varies the threshold in accordance with the performance variation. Thus, the speakerphone of the invention achieves a stable communication system that approaches to the fill duplex with the voice switching system and the echo canceling system combined.