The main purpose of this study is to develop a numerical analysis code for the prediction of a flapgate breakwater behavior during a huge tsunami. The features of this code are that the FAVOR method and the VOF method are applied. The code is applied to a hydraulic experiment of flapgate breakwater. As a result, the obtained numerical solutions agree well with the result of the experiment. Furthermore, through applying the code to a prediction of the flapgate breakwater behavior during the 1993 Hokkaido-Nanseioki tsunami, the applicability of the code to a real-scale simulation and the effectiveness of the breakwater to a huge tsunami are discussed.
