PURPOSE: To generate power while saving the resource by installing a tubular power generating chamber in a reservoir, then discharging the water from the power generating chamber into the reservoir and circulating the water while installing a generator for utilizing the circulating water in the power generating chamber.

CONSTITUTION: A tubular power generating chamber (a) is arranged in a reservoir 12 storing the water, then the water taken through a water take-in port 1 made at the upper section of said chamber (a) is fed to a generator 2 in the power generating chamber (a), thus generating power hydraulically. The water used for power generation and stored in a water storage tank 3 at the lower section of the power generating chamber (a) is led through a pipe arranged with a valve 8 to a water discharger 4, then the water is discharged into the reservoir 12. The interior of the water discharger 4 will serve as an air chamber and can accumulate the air pressure in accordance with the height of the water discharger 4.