Listening to music at concert is different from listening to it from CD player. It is caused from not only sound facilities, but also interaction between player and listener. In this research, we investigated relation between listener's respiration and music to analyze interaction in live performance. As a result, it was discovered that listener's respiration period was changed by music, and also player's 1-bar period was changed by listener, and it was suggested that mutual entrainment occurred between 1-bar period and respiration period.