Abstract: Beach erosion at Oarai Beach caused by extraordinary waves and large sea level rise during a low pressure occurred on October 7, 2006 was investigated. On this beach, the shoreline has retreated since 1984 due to decrease in sediment supply from the Naka River. Also seawall was advanced seaward to expand the parking lot for Oarai Aquarium. These events triggered heavy damages of seawall and formation of high scarp invading the coastal park. The anthropogenic factors were studied in detail.