PURPOSE: To improve the precision in detection by compensating the effect produced on an output of a differential pressure detecting part by a change in the permittivity of a sealed-in liquid due to a static pressure of each introduced pressure.

CONSTITUTION: A strain sensor 61 is attached with its sensing direction made to coincide with the radial direction of a protective diaphragm 3, and a static pressure compensating part 71 executing static pressure compensation on the basis of an output of the strain sensor 61 and an output of a differential pressure detecting part 20 is provided. A strain in the radial direction detected by the strain sensor 61 is the sum of the strain due to a differential pressure and the strain due to a static pressure. When the static pressure is much larger than the differential pressure, accordingly, the strain in the radial direction can be regarded as corresponding to the static pressure substantially. The effect on the output of the differential pressure detecting part 20 produced by a change in the permittivity of a sealed-in liquid due to the static pressure of each introduced pressure is compensated by the static pressure compensating part 71. By selecting the place of attachment of the strain sensor 61 to be the place of the radius Ro where the strain in the radial direction due to the differential pressure is zero, besides, the sensor can be made to correspond exactly to the static pressure.