PURPOSE: To improve the efficiency of a plant by providing a tray type water heater in the sea water and taking out hot surface sea water heated by the rays of the sun while sea water is passing through the water heater.

CONSTITUTION: A sea temperature difference power plant P takes out hot sea water through a pipe 11 having an opening in hot surface sea water in a tray type water heater T by means of a pump 10, and allows a low boiling point medium to evaporate by means of an evaporator 12, making the evaporated medium drive a turbine 14 through a pipe 13. The hot water is again returned to the tray type water heater T through a pipe 20, heated by the rays of the sun while it flows in the tray, and circulated with a raised temperature, thereby improving the efficiency of the plant.