The Oubaku fault is an active fault bounding the south-eastern edge of the Kyoto Basin. Although the structure of the fault was inferred to be reverse by the past several reports, the vertical displacement of it has remained unknown and the inferred strikes have been different author by author especially in and around Gokasho, Uji. In order to know more precise subsurface structure of the Oubaku fault, we carried out a seismic reflection exploration and drilled two boreholes (130 m and 400 m) with several geophysical explorations at Gokasho, Uji. The result of the seismic reflection exploration showed the existence of a reverse fault, as had been inferred before. The vertical displacement of the fault is about 170 m and the orientation of the strike is NNE-SSW. The other several faults are also recognized but the vertical displacements of them are much smaller. The subsurface structures of them mainly show the characters of reverse faults but they are more complicated than expected before.