Abstract: The inventions relate to measurements of a hydrostatic and/or fast-changing pressure by optical means, and are suitable for aerodynamic investigations of aircraft and small spacecraft, in robotics, including small force micro-clamps, in remote pressure monitoring (in wells, vessels, cylinders), in medicine and medical and biological investigations, hydroacoustics, security systems. The object is to improve the sensitivity and enhance the temperature and vibration stability of a pressure sensor. The pressure sensor is a low Q-factor Fabry-Perot cavity/interferometer 6 at the end of a single-mode optical fiber 1 with the 4% Fresnel reflection from the silica glass/air interface. Another movable mirror of the cavity is formed by an end face 10 of a short (1-3 mm) optical fiber length 9 having a small inertial mass and inserted into the center of a flexible membrane 9 of 500-700 &mgr;m in diameter, tightly sealing a small air volume of about 1-3 mm3 inside a second capillary 3 with the external diameter of 0.