This paper presents some knowledge of vibrations caused by actions of a large audience during concert is given. Firstly, full investigation was made into relationships between vibrations, actions of audience and music programme of a concert. From this investigation, it was made clear that main cause of the vibration was "TATENORI" action "TATENORI" action was done by audience when rhythms of performed music became quick (about 2-3 Hz). Secondly, from the relationships between experimental and analytical investigation, exciting force of "TATENORI" action was estimated. One time history curve was obtained as the exciting force, which was composed of triangular pulses.
