The planting experiment was conducted using two kinds of floating plant boxes at the down stream region of Wakagawa-river where the average river water salt concentration should set 2.0 % or more.The structure of one type of floating plant box using river water type was as follows; The soil layer undersurface receives moisture supply in contact with the river water surface. The next type of floating plant box using rain water type was made to dissociate from the water surface and let only rain be the source of water supply of water.