Beach changes on the Shizuoka and Shimizu coasts with a gradually-curving shoreline along Mihono-matsubara sand spit were predicted using the BG model and employing the real coordinate system instead of expanded coordinate systems. On these coasts, many detached breakwaters with short offshore distances and five artificial headlands have been constructed as a measure against erosion. By this calculation, overall beach changes of these coasts associated with the movement of a sand body were reproduced, including the change in shoreline position and longitudinal profiles. The effect of beach nourishment until 39 years from the present was predicted. It was confirmed that beach nourishment at a rate of 8×10⁴ m³/yr is required on the Shimizu coast to maintain or recover a sandy beach.