A large-scale coastal erosion was caused in Hasaki coast by the storm caused by low-pressure passing in October 6th - 8th, 2006. The coast was eroded not only the foreshore but also the backshore, because storm surge was caused simultaneously at the flood tide. Appearances of the coastal erosion are clarified by using the topographic data before and after the storm and the image during the storm. The large-scale backshore erosion is caused in three steps as follows: First, the foreshore is eroded and the berm disappears completely. The beach profile is formed to the gentle foreshore and following the steep backshore. Next, the wave runs up on the steep backshore. The down-rush flow cuts the backshore, and the beach scarp is partially caused. The third, the run-up waves come directly to hit the base of the beach scarp, and the beach scarp grows up widely. The situation of the beach scarp erosion is different in the beach profile before the storm. In the backshore that accumulates up in enough height by the effect that coastal vegetation hold blown sand, the second step is not caused.