To install an inexpensive pumping device for hydraulic power generation in a plain land.

Water for power generation after use is stored in a primary water tank shown in the figure, the water is flowed into chambers F, G through a suction water pipe, and an inlet port of the chamber F is closed to seal the chambers F, G. Compressed air in a rubber bag A1 including lead of the chamber H is discharged by a vacuum pump, so that total volume of volume of A1 under water in the chamber H and volume of a box K under water in the chamber G is made to be smaller than total weight of weight of the box K connected with the rubber bag A1 and weight of the rubber bag A1. The box K is pulled down, and the water in the chamber G overflows through an inlet 9 shown in the figure into a water passage 2 intermittently once every two minutes by 420 m3 for each time, so that the water of 3.5 m3 per second required for generating power of approximately 1,440 KW is circulated to solve the problem.