The Port and Harbour Research Institute has been developing a wave power converter named as a wave power extracting caisson. The caisson is used as a breakwater caisson. The design method of the caisson was proposed through the basic researches by the institute.
　The First District Port Construction Bureau and the Coastal Development Institute of Technology with twenty private enterprises conducted a field experiment of wave power exetracting caisson breakwater at Sakata Port in Yamagata prefecture. The experiments were conducted successfully from the winter of 1989 to the winter of 1991. In the experiment the wave activated power conversion was made and several kinds of mesurements were performed. This report describes the rusults of data analysis of the field experiment. The incident wave power, the stability of the caisson and the efficiencies of the converter are discussed in the report.