The estimation of the incident wave power is essential in the deisgn of any system of wave energy utilization. The Bureau of Ports and Harbors of the Ministry of Transport and other organizations in Japan are conducting wave observations throughout the nation. In this note, the quantity of the wave power around Japanese islands is briefly described based on the observed data. The quality of the wave power, that is its variation, is also discussed.
　The average of the total amount of the wave power around Japanese islands is 36 million kW. The wave poweer is large in the middle and northern part of the Honnshu Island along the Pacific Ocean coast and along the Japan Sea coast. The variation of wave power is very intensive. Especially the wave power in the Japan Sea side have very clear seasonal change.
　This variation hinders the utilization of wave power There is no index to describe properly the influence of the variation on the wave power conversion. In the note, sumulations of a wave energy converter are conducted to calculate its output based on the observed wave data, and several practical indices are obtained concerning the fluctuation of the output power of the converter from the simulation.