This paper discusses a conference state estimation method that uses only biosignal processing; linguistic understanding is avoided. In conventional dialogue communication research, the physiological characteristic of "entrainment" between the participants has been already reported. We extend "entrainment" to introduce the concept of "resonance" to grasp the relationship between attendees. We then propose a method which estimates the conference state from "resonance". First, using a multimedia conference system, we record conference data including time-series records of heart rate. By observing and analyzing the conference data, we assess the "resonance" phenomenon among the talkers. Using the "resonance correlation matrix", a newly proposed index based on the correlation of the heart rate data, conference participative state can be successfully estimated.