7. The system according to claim 6 , wherein the classifier classifies a conversation between the first speaker and the second speaker based on the smoothed difference data string from which at least one of a start portion and an end portion in the conversation between the two persons is removed.
6. The system according to claim 2 , wherein the first variation calculator calculates the variation of the speech ratio of the first speaker from the voice data representing the voice of the first speaker in a conversation in which the first speaker and the second speaker speak by phone, and the second variation calculator calculates the variation of the speech ratio of the second speaker from the voice data representing the voice of the second speaker in a conversation in which the first speaker and the second speaker speak by phone.