Many breakwaters were damaged by the Great East Japan Earthquake of March 11, 2011. Many of these were destroyed under tsunami overflow. Some results of researches indicated that in the case where scouring of the foundation had occurred, the safety factors for bearing capacity failure declined to less than in a case where the foundation part was not scoured. But, the relation between the overflow and scouring depth had not been clarified. In this study, the scouring depth due to tsunami overflow was investigated by using the physical model tests. Results pointed out that the scouring depth can be evaluated by the scale of vortex due to overflow.