This study describes the nonlinear vibration response of a cylindrical water storage tank caused by coupling effect between the beam-type and the oval-type vibrations. The results of the frequency sweep tests with the large input acceleration demonstrate the resonance frequency of the tank shifts to the lower frequency region and the magnification factor is smaller. Considering the out-of-plane of the tank-wall induced by the oval-type vibration, a simplified model having the spring constant dependent on the amplitude of the oval-type vibration is proposed, and then the numerical simulation using this model is conducted.