To investigate a function of the setback-type floodway, a movable-bed experiment using a plane wave basin was carried out, while changing the discharge of the floodway. It was found that the formation of a small stream in the berm was possible when the discharge of 0.3-0.8 m3/s was given from the floodway. Also, the berm was completely washed away given the discharge over 10 m3/s. Furthermore, offshore sand transport prevailed and part of longshore sand transport was blocked with the discharge of 150 m3/s.