The construction of tsunami breakwater was proposed in several harbours after the disaster due to the Chilian Earthquake Tsunami in 1960. Our laboratory examined the effect of those breakwaters against tsunami with numerical computation of which the method of analysis and results obtained were presented to the 10th Conference on Coastal Engineering.
　On May 16,1968, the northern part of Japan was attacked by a severe earthquake of Magnintude 7.8, which was accompanied with a remarkable tsunami. One of authors presetned the results of numerical computations on the effect of Ofunato Tsunami Breakwater against 1968 Tsunami to the 13th Congress of the I.A.H.R. in 1969. In this report, the authors applied the method of analysis to Hachinohe Port, which often suffers from damages caused by tsunami. At the time of 1968 Tsunami, a part of breakwater over 300 m in total length was destroyed due to considerable difference of outside and inside water level.
　The computations were carried out for several topographic conditions, including the present, the past and the future status of Hachinohe Port with the incident tsunami of sinusoidal wave trains and of an irregular profile.
　Computed results made clear the behaviour of tsunami and the effect of breakwaters against tsunami in Hachinohe Port. It also shows remarkable difference of water level between inside and outside of the destroyed breakwater.