A three-dimensional seismic velocity structure in the edifice of the central cones of Aso Volcano is obtained from a tomographic inversion to seismic data of a controlled source experiment ASO98. The three dimensional P wave velocity structure with dimensions of 12kmÅ~9kmÅ~2km is derived from 1207 P-wave first arrivals at 296 temporary stations for six explosions. The entire velocity structure obtained includes higher velocities than those of any previous velocity models down to 0.5km of altitude above sea level. A high velocity zone and a low-velocity zone are revealed in the obtained velocity structure. The high velocity zone lies toward WSW direction from the active crater. The strike of this high velocity zone is coincident with the general alignment of the central cones and with a trend of the high gravity anomaly in this area. The high velocity zone is inferred as dykes or volcanic deposits with dense materials from its coincident location with the high gravity zone and drilling core samples in the vicinity. The low velocity zone is located in the northwest flank of the central cones. The low velocity zone implies deposits with low density and low velocity material beneath the northwestern flank.