Probability density of the maxima of irregular oscillation, whose instantaneous values are distributed exponentially, forms a exponential distribution, and its cumulative value becomes also as well. Such a type occurres in long-term record of voyage under various weather conditions during several months or several years. The properties of this distribution are that the maximum frequency apears at the position of amplitude is zero, and that the critical maximum value is about twice as large as the mean value. The period of prominent high value is macroscopically almost constant.