It is important to estimate proper initial stiffness of seismic isolation device to evaluate effects of environmental vibration assessment. We examined stiffness properties of the seismic isolation device in infinitesimal deformation range by using dynamic lateral experiment results. It was found that the initial stiffness of seismic isolation device is 20 times the stiffness of the 100% strain. and that equivalent stiffness decreases rapidly when the strain is over 0.3%. Finally, we propose a simple method to estimate the vibration level of seismic isolation against excitation force inside buildings.
