A joint dense seismic observation experiment was conducted during the period of September 2002～April 2005 in cooperation of researchers of national universities under the national project for prediction of volcanic eruption. Major objectives include seismic exploration of the subsurface structure of Fuji volcano and surrounding area as well as array observation of deep low frequency earthquakes, the activity of which increased in 2000－2001 beneath the volcano. We installed 28 seismographs temporarily on and around Fuji volcano and the data was transmitted to the Volcano Research Center (VRC), Earthquake Research Institute by satellite, radio and cable telemetry systems. We further collected seismic data of permanent stations around Fuji volcano operated by related research institutions. All the data was collected and picked at VRC. In this initial report we describe the brief outline of the joint experiment, and summarize the preliminary results of analyses on the seismic velocity structure of Fuji volcano and wave characteristics of a low frequency earthquake, which occurred on 11 September 2003.