The Fukuchiyama fault system consists of two faults named the Tonda fault at the northern part and the Fukuchiyama fault at the southern part, The Fukuchiyama fault system has been activated as a reverse fault with relative subsidence of the eastern mountain area. This fact shows the activity of the Fukuchiyama fault system has been the reactivity along the scar of the“Geologic Boundary Fault”between Paleogene and Paleogene or Mesozoic basements. The reverse activity has occurred after the formation of higher terrace in the middle Pleistocene. As a result of the trenching study, the latest activity of the fault system occurred at 11,000 - 25,000y B. P. with 0.6m vertical offset.