The invention concerns a pressure sensor (5), particularly for a depth gauge (1), capable of having a high level of precision, owing to sufficient elastic deflection amplitude of the diaphragm (or membrane), while avoiding any risk of plastic deformation. The diaphragm (12) is formed by a flat metal disc. The peripheral region (13) thereof is neither welded nor inset, but it is pre-stressed against a stop strip (25) with a closed, preferably circular contour, and can pivot on the stop strip (25) when the diaphragm bends under the effect of fluid pressure in the pressure chamber (10). The pre-stressing may be achieved via a sealing gasket (21) located opposite the stop strip (25). Between said strip and a central aperture (15), a concave stop surface (20) limits the deflection of the diaphragm (12) and prevents any plastic deformation in the event of excessive pressure. Manufacture of the diaphragm is simple, with a high level of reproducibility, assembly is easy and the seal quality is high.