PURPOSE: To enable to measure a low differential pressure of 1,000mm or less of H2O and perform the measurement of good linearity by a method wherein a thick beam part which connects a peripheral fixed part and a central rigid body is provided at a groove part corresponding to the position whereat a piezo resistance element is formed on the surface.

CONSTITUTION: The diaphragm main body 1 formed of a semiconductor single crystal of Si or Ge, etc. has the thick peripheral fixed part 2, the likewise thick central rigid body 3, and the groove part 4 provided between the peripheral fixed part 2 and the central rigid body 3. The piezo resistance element 6 for pressure detection purpose is formed at the position corresponded to the center of each side of the groove part 4 on the surface of the diaphragm 1, and further the beam part 7 which connects the peripheral fixed part 2 and the central rigid body is provided at the groove part 4 corresponding to the position whereat this piezo resistance element 6 is formed. The diaphragm main body 1 wherein the groove parts 4 are formed has a thin part, and the position whereat the beam part 7 has the same thickness as the peripheral fixed part 2 and the central rigid body 3. Thereby, the linearity is improved.