PURPOSE: To raise the efficiency of energy conversion by making the density of gas higher by turning a generator in a closed cycle consisting of left and right tanks and a pipe.

CONSTITUTION: When being tilted by tidal wave to cause a positional shift, the liquid 7 in the tank 3 is passed through the connection pipe 5 to pressurize the gas 6 in the tank 2, and then the gas 6 thus pressurized is jetted as a jet stream into the tank 3 repeatedly. In this case, if the turbine 8 is provided inside the pipe 4 for gas, the shift of the gas turns the turbine 8 and thereby the generator 9 connected to the turbine 8 is turned to generate electric power. In the left and right tanks 2 and 3 which are formed in a closed cycle by the connection pipes 4 and 5, pressure is raised and therefore the efficiency of energy conversion can be enhanced.