PURPOSE: To eliminate environmental pollution, keep safety, and reduce cost.

CONSTITUTION: A power generator consists of a water taking-in case 3, a buoyancy case 7 provided in the water taking-in case 3, an expansible air compressor 6 on which the water taking-in case 3 is mounted, a vertical pump 11 for pumping water which flows out from the water taking-in case 3, and the like. Rising motion by buoyancy of the buoyancy case 7 and flow of water which flows out from the water taking-in case 3 are changed into rotary motion, and the rotary motion is transferred to a main shaft 1 so as to obtain power source of all machines, a power generator, and the like.