Breaking wave forces on a circular cylinder are measured using regular and irregular waves. Strains on a model cylinder caused by the impact forces are also measured. A calculation method of impact forces by breaking waves on a cylinder is proposed on the basis of the experimental results with some theoretical considerations.
　In the calculation method, the impact force is assumed to act the upper half portaion between the still water level and the wave crest with a triangular distribution along the cylinder axis. The peak value fpm in the distribution is expressed by νfkm, where ν is adjustment factor and fkm is the peak value given by Karman's theory. The adjustment factor is determined by the experimental results and is indicated by the function of newly defined breaking force parameter and cylinder inclination.