On 13 November 2009, suddenly an accident occurred in which a fast RO/RO ferry was greatly inclined to the starboard side in quartering sea. The Japan Transport Safety Board (JTSB), Ministry of Infrastructure, Land, Transport and Tour-ism looked into this incident, and reported the results of survey. That report was including estimated conditions of ship at the incident and wave, wind so on. In order to take measures, clarification about mechanism of this phenomenon is important. In order to know what had happened, the authors carried out a model experiment reproducing the incident at Actual Sea Model Basin, in National Maritime Research Institute, Japan.