Ariake Sea, a typical closed bay on the west of the Kyushu Island, is a sea area where a vast tidal flat develops. Recently, various environmental degradations are reported occur in Ariake Sea, as red tidal and anoxic water. In this study, the ecosystem formation process by recovery of shore line, the aim in this method is to establish the technology that can artificially restore the tidal flat and the shore line in front of embankment development and to recover and maintain the ecosystem, was investigated in Ariake Sea. One year passed after shore line was constructed; benthos species has increased by the twice or more. The effect in the future can be expected by recovery of shore line.