PURPOSE: To obtain power generation by a constitution wherein an inside vessel having two water chambers provided with a valve operated automatically by rotation and a weight and also a weight is placed in a rotary vessel, and the inside vessel is filled with water around.

CONSTITUTION: An inside vessel 2 having two water chambers 3, 5 and a weight 8 is placed in a rotary vessel 1 turning on an intermediate shaft 4, and inside vessel 2 is filled with water around, the two water chambers are connected through with a channel pipe 8, and air inlet valves 9, 10 rotating automatically by rotation of the inside vessel 2 and covers 11W14 are provided on both water chambers 3, 5. When the inside vessel 2 rotates according to buoyancy, the air inlet valves 9, 10 and the covers 11W14 operate according to its rotation, and water in one of the water chambers 3, 5 flows into the other chamber, therefore the inside vessel 2 is kept rotating to obtain power generation.