Abstract: [Problem] To provide a marine power generation system which is engineered to be able carry out power generation stably and highly efficiently, using the large source of energy even in ocean currents having insufficient speeds to create a water current, similar to a water discharge from a dam, which is ideal for hydroelectricity. [Solution] As an example of a water intake structure (10), a sea surface floatation object, floats on the sea by buoyancy, and has an aperture part (12) through which seawater is taken therein. A water guide pipe (20) is underwater, which secures a space underwater. One end of the water guide pipe (20) is connected to the sea surface floatation object (10), and the seawater which is taken in from the sea surface floatation object which is the water intake structure (10), is introduced downward under the sea surface.