The conventional Boundary Element Method (BEM) employing free-surface Green's function is practically impossible to be applied for large-scale analysis such as wave diffraction/radiation analysis for Very Large Floating Structures (VLFS) in general sea-bed topography. This is mainly due to O(N^2) requirement for storage and O(N^3) characteristics for CPU time, where N is the number of unknowns for the BEM. The Fast Multipole Algorithm (FMA) has thus been applied to the BEM utilizing the Green's function by the present authors. The method has O(N) characteristics both for storage requirement and CPU time. The method has been applied to large-scale analysis such as wave response analysis of pontoon type VLFS in general sea-bed topography, and hybrid-type VLFS having complicated shape, where N is the order of 10^4 - 10^5.