A very large floating structure has hydro-elastic responses that are an elastic deformation and a slowly varying drift motion. Generally, a breakwater is established to reduce the responses. However, it is very difficult to construct it from technical point of view and costs when the water depth increases. Therefore, it is necessary to develop the response reduction system for a very large floating structure even in open seas. In this paper, a new hydro-elastic responses reduction system of a very large floating structure by using wave energy absorption devices has been proposed. The characteristics of hydro-elastic responses of an elastic structure with wave energy absorption devices were investigated both experimentally and numerically. This new system was proved effective in reduction of hydro-elastic responses of a very large floating structure. Two numerical analysis methods were developed to estimate hydro-elastic responses of a very large floating structure. The results obtained by these methods give a good agreement with the experiment results.