Strain Detector and method of manufacturing the same

A fluid pressure sensor (1) for measuring the pressure of a fluid comprises a diaphragm portion (12) which is a strain generating body, a silicon oxide film (21) as an insulating film, and a strain gauge (20) made of crystalline silicon, and austenitic precipitation hardening type Fe-Ni heat-resisting steel excellent in mechanical strength and corrosion resistance is used for the diaphragm portion (12). The silicon oxide film (21) is formed with the internal stress thereof adjusted to the range from -150 to 130 MPa. With this feature, the fluid pressure sensor (1) ensures high precision and reliability, and may be used even for measurement of a highly corrosive fluid.