PURPOSE: To simplify the structure while enhancing the durability by controlling the liquid level of a high pressure liquid over a wide range using a totally mechanical means thereby eliminating the need of electric/electronic controller and level detector.

CONSTITUTION: Flow rate of a gas flowing through a duct 1 via an orifice 2 is substantially constant and a pressure difference P-P1 appearing between first and second chambers 7, 8 communicating with each other through orifices 5, 5a, 6 acts to displace a valve member 10. Position of a movable comparison element, a valve rod 11 and a valve member 10 can be adjusted by regulating tension of an urging spring 15 through an adjusting screw 16. When a liquid level regulator is in normal working state, the valve member 10 is not seated on an orifice 4 and kept at such opening as a small quantity of gas can be discharged to the outside. When such a mechanical liquid level measuring apparatus is employed, liquid level of a high pressure liquid can be controlled accurately over a wide without requiring any electric/electronic controller or level detector and thereby the structure is simplified while enhancing the durability.