Water cycle facilities are usually constructed at coastal area because of sewage collecting system by gravity flow. So, seismic performance against not only earthquake motion but also tunami should be secured. In this study, we have proposed isolation structural method against strong earthquake motion and wave force of tsunami by utilizing asphaltic viscous fluid isolator. Effectiveness of the proposed method was examined by three-dimentional FEM analyses. As a result, it is considered that stress within the structure induced by earthqauke motion and tsunami can be largely reduced by buffer effect of isolator.