PURPOSE: To provide the method which economically and speedily controls the liquid level position in the liquid tank containing a certain amount of liquid into a specific range and the liquid level control mechanism.

CONSTITUTION: (i) A liquid level detector 21 detects the liquid level position in the liquid tank. (ii) The liquid level position signal obtained by the liquid level detector is inputted to a controller 20. (iii) The liquid level position signal inputted to the controller is converted into the operation signal of a flow rate control valve according to the predetermined relation between the liquid level position and the opening extent of the flow rate control valve 15. (iv) Gas is admitted to the liquid tank through the flow rate control valve operated with the operation signal of the flow rate control valve obtained by the controller and jetted into the liquid through a gas jetting device 17 in the liquid tank.