A research and development on “Density Current Generator” which is a new concept machine to agitate and upwell the stratified water area widely and calmly by using a density current is carried out. The machine draws water from top and bottom layer of the water area, and the vertical pipes of the machine lead both top and bottom waters to the pump casing located on middle layer of the water area. Two different waters are mixed up and blown off horizontally via the ring-nozzle by the motor-driven impeller installed in the pump casing. The mixed water is diffused toward every direction on the horizontal plane as a density current which is driven by gravity. A model test and study using the law of similarity was carried out to predict the performance of the full scale prototype machine, which is working in Gokasho Bay, Mie Prefecture Japan since June 1997. The result of performance measurement is that the density current of 120, 000 m³/day is generated by electric power of only 12 kw, and the water area measurement is that the significant changes of sea water qualities are observed. Although further study should be needed to verify that these changes are caused by the machine, it is clear that the machine widely influences on the environment of the water area. These results lead us to believe that the Density Current Generator has excellent potential in terms of agitating and purifying stratified water of very large area.