The Paleogene Kobe Group in the Sanda Basin, southern Hyogo Prefecture, is composed mainly of non-marine clastic rocks, such as conglomerate, sandstone, mudstone and tuff. We made a stratigraphic survey of the group in the southwestern part of Tojo-cho, Kato-gun, Hyogo Prefecture, based on detailed tracing of tuffs. Four tuff layers were discerned within the Yokawa Formation of the group' the Ansei-ike, Yabu, Shinjo and Shikahori-ike Tuffs, in ascending order. As a result of our precise tracing of these tuff layers, we clarified that the Yokawa Formation in the study area inclines gently southward, although previous researchers have proposed a westward-inclining structure.