The effect of breakwater on reduction of tsunami inundation is investigated for the tsunami caused by the 2011 off the Pacific coast of Tohoku Earthquake. Numerical simulations are conducted in the Port of Kamaishi and Port of Ofunato and Port of Soma in which bay-mouth breakwaters and offshore breakwater are installed. It is confirmed that the bay-mouth breakwater in Kamaishi and offshore breakwater in Soma reduced the area of tsunami inundation and its height, although they were damaged by the tsunami. The reason why they reduced tsunami impacts is that caissons remain partly and mostly. In addition, the numerical simulation indicates that the breakwater mound has the effect on reduction of tsunami intrusion for the bay-mouth breakwater in Ofunato.
