PURPOSE: To make the indicator usable for high pressure liquid as well by providing a piezoelectric transducing element between a hermetically-sealed chamber at which a solid float is connected to the center of a diaphragm and another hermetically-sealed chamber having a diaphragm for back pressure.

CONSTITUTION: The hermetically-sealed chamber 16 is formed of the diaphragm 15 to which the solid float 24 is connected by a rod 23 and of a housing 10. At the back from the chamber is provided the piezoelectric transducing element 26, which is connected to a lead pin 28. A chamber 19 located on the opposite side of the piezoelectric transducing element 26 is communicated with the hermetically-sealed chamber 18 formed by the diaphragm 17 for back pressure through a passage 22, and non-compressible silicone oil is enclosed in the two sealed chambers. The gravity of the float 24 is adjusted by a spring 25 and thereby a zero position is set. When a level rises, the float 24 presses the diaphragm 15, thereby the pressure in the sealed chamber 16 is increased and, based on the differential pressure between the chamber 16 and the chamber 18, the piezoelectric transducing element 26 detects a signal. Even when vapor pressure rises, the diaphragms 15 and 17 are balanced and thus no output comes out. By this method, the level indicator of high sensitivity and high precision which withstands high pressure liquid can be manufactured.