The large-sized, multi-walled coaxial cylindrical tank has been studied in recent years because various kinds of oil can be stored in one tank It is important to design such tanks considering seismic response. This paper describes theoretical studies of the coupled vibration of the contained liquid and the shell plate of the cylindrical tank in response to lateral earthquake excitation, by the finite element method. In this paper, the bulging motion which occurs in the relatively high frequency region due to the flexibility of the shell is analyzed. The natural frequency the time history of the displacement response of the shell and the dynamic pressure response of the liquid of the actual tank are derived by the modal analysis approach.