The supposed wave condition has direct effects upon the theoretically estimated extreme value on the long-term distribution of wave induced variable of a ship. So, the accuracy of the estimated value is not reliable in the case when the visually observed wave data are directly applied as the supposed wave condition. Authers studied on the statistical characters of wave statistics in the North Pacific Ocean by 163 th Research Committee of the Japan Ship Research Association which are the most reliable wave data observed there. It is showed that the frequency distribution of both wave height and period can be described by the log-normal distribution. The theoretical distribution of wave height appears to be valid in range of the cumulative probability up to 0.99999. The method of the correction of the observed wave statistics is indicated. Applying the theoretical distributions, the original wave statistics in the North Pacific is corrected. The wave data introduced by the correction are the most reliable data of the sea zone to be supposed in the theoretical estimation of wave induced valiables.