Long-term beach changes of the Ryuyo coast facing the Pacific Ocean were investigated through the comparison of the aerial photographs. Beach erosion has been severe on this coast as well as the excess sand deposition at Fukude fishing port located downcoast. As a measure against excess sand deposition, sand-bypassing is planned at this fishing port. Under these conditions, three-dimensional beach changes were predicted using the contour-line-change model proposed by Serizawa et al.(2002), taking the coastline with a 17.5 km length between the mouth of the Tenryu Riverand that of the Benzaiten River as the example, and the impacts of the sand-bypassing and decrease in fluvial sediment supply to the surrounding coastline were investigate