In order to investigate subsurface density structures with the highest precision, two major gravity databases and some unpublished data files, which cover Southwest Japan, are recompiled. This paper presents some examples of the detailed gravity anomaly maps in Kyushu District, southwest Japan. These maps indicate various fine subsurface structures, which may arose with tectonic movements and/or volcanic activities of this region. With an aid of geological and topographical information, we discussed relationships between characteristic patterns of the detailed gravity anomalies and subsurface structures in this region. The most conspicuous feature is an existence of a steep horizontal gradient zone of gravity anomalies running through the Aso Caldera in the ENE-WSW direction. Although the location of the westward extension of the Median Tectonic Line (MTL) in this region is still debatable, this zone seems to be the westernmost part of MTL.