This paper deals with a large scale pontoon-type structure such as floating airport. For analyzing the wave response of such large scale structure, the effect of the structural flexibility on the fluid-structure interactions should be considered. The proposed analytical method employs the Boundary Element Method for evaluating hydrodynamic forces (wave-excitation force, added-mass force, and hydrodynamic-damping force), and the Finite Element Method for calculating wave response of the elastic floating body. The experiments are performed for the 2-D model structure made of polyurethane plate and having the length of 10 m, the width of 0.5 m, and the thickness of 76 mm, 38 mm, and 19 mm. Some numerical examples for the 2-D structure are presented and are compared with the experimental results.