This paper deals with i) the roles of floating wave power plant in the control of environment of coastal waters for coastal fisheries, ii) experimental investigation of physical characteristics, i. e. waves and wave induced nearshore current around a model of the floating wave power plant on inclined bottom comparing with those around a model of detached breakwater from the viewpoints of creation of calm water areas and water exchange. The results of this paper are summarized as follows. (1) The floating wave power plant can be utilized from the viewpoints of environmental conservation and progress of coastal fisheries for creation of calm sea areas, improvement of water quality and control of nearshore current, and power for aeration and dipping out of bottom waters. (2) The calm water area behind the floating power plant model where wave transmission ratio is less then 0.5 in three dimensional condition is almost the same as behind the detached breakwater. (3) The above mentioned calm water area becomes wider near the shore line as the bottom slope becomes more gentle. (4) The reflected wave height at the front of the floating power plant model is much smaller than the detached breakwater. (5) Circulating current on free surface from the center of the model to outer side in the case of floating power plant model is dominant near water surface, on the contrary, it is dominant from outer side to the center of the model in the case of detached breakwater. In particular, strong current toward shore line just behind the floating wave power plant model was observed. (6) Water exchange near the floating wave power plant model is larger than the detached breakwater. It becomes larger as the bottom slope becomes more gentle for both models.