This paper focuses on the method of designing structures against liquefaction and a subsequent lateral flow. Shaking table tests and analyses were carried out to clarify the mechanism of pile stresses caused by the liquefaction-induced lateral flow. As a result, it is proved that the design of structure against liquefaction shall reflect changes in the natural frequency while considering the additional inertia force of liquefaction ground. It has also become possible to economically design structures by assuming that the liquefaction-induced lateral flow is a ground displacement force.