Through an idealized modeling experiment, in which the East Sea is simplified as a small rectangular basin with a through flow placed at the upper left corner of a larger basin, the effect of the Tsushima Warm Current on the East Sea has been investigated. The NOAA/GFDL MOM V.3 is used. The horizontal resolution is 0.25° both in the zonal and meridional directions. The basin is 4000 m deep, and there are 36 depth levels in the vertical. The effects of surface wind stress are also considered by conducting experiments with or without a zonal wind stress.