To provide a marine power generation system for generating electric power, by making a water flow required for hydraulic power generation, by using large energy even in an ocean current of insufficient flow speed.

On the sea, an ocean floating body 10 has an opening 11 for taking in seawater. The seawater is guided inside the ocean floating body 10 via a conduit pipe 20. A generator 30 is arranged in the conduit pipe 20, and generates electric power by pressure of the ocean current and water pressure by a head of a water surface generated inside the conduit pipe 20. There is a storage space 40 inside, to provide a space for taking in the seawater. This storage space 40 exists under the sea surface. The seawater taken in the storage space 40 is discharged outside the storage space 40 by a discharge part 50. When the ocean floating body 10 is formed in the size of a super-huge tanker, the seawater is jetted inside from the opening part 11 arranged in a bow part of forming a huge wall surface, and a structure as if arranging a large dam in the vicinity on the sea is provided, and hydraulic power generation like a large dam can be performed.