The Naruto-South fault is situated of about 1000m south of the Naruto fault, the Median Tectonic Line active fault system in the eastern part of Shikoku. We investigated fault topography and subsurface geology of this fault by interpretation of large scale aerial photographs, collecting borehole data and Geo-Slicer survey. The results obtained are as follows; 1) The Naruto-South fault runs on the Yoshino River deltaic plain at least 2.5 km long with fault scarplet. the Naruto-South fault is oblique by about 5-10°clockwise to the strike of the Naruto fault.2) Geologic boundary (MTL) suggested by borehole data, extends between Himeta and Ote-Beach about 8 km long, buried under alluvial deposits.. The strike and location is consistent with the Naruto-South fault and submarine fault. Therefore, the Naruto-South fault is presumed to have dislocated using the part of fault plane of the geologic boundary fault.3) We investigated to detect marks of the last faulting event by use of Geo-Slicer, and we confirmed a active fault with lateral slip component.