Taking Shichiri-ga-hama Beach facing Sagami Bay as the study area, beach changes since 2007 were reproduced using the BG model, and the effect of beach nourishment as a method against beach erosion was studied. Since rocky bed extensively distributes beneath the sandy beach, return flow during the wave run-up can be strengthened, accelerating seaward sand transport. Therefore, considering that the return flow causes the decrease in equilibrium slope, such a mechanism was included in the BG model. Moreover, wave direction seasonally changes on this beach, so that such an effect was also considered. As a result, it was concluded that recent shoreline recession near the east end of Shichiri-ga-hama Beach was well reproduced. Furthermore, to recover sand beach in this area, beach nourishment at a rate of 5,000 m³/yr is needed.