To take out a large capacity of electrical energy and easily obtain optional high voltage with a compact system in a power generation system utilizing salinity difference between fresh water in rivers or the like and salt water in seas or the like, both of which exist almost infinitely.

The system uses such a configuration that electric short-circuit through a water-supply channel and a water-discharge channel is prevented by falling fresh water and salt water as water drops respectively to utilize the insulation performance of air or by interposing a valve using a valve body, a valve seat and a valve box, all of which are made of an insulating material, and thereby, electric short-circuit between a plurality of cells generating unit electromotive force is prevented.