A pressure sensor has a housing in which at least two diaphragms are secured in such a manner that they include a volume which is filled with a hydraulic fluid. The incompressible hydraulic fluid serves to transmit pressure between the diaphragms. For introducing the hydraulic fluid one diaphragm is provided with an opening. A narrow tube is connected in fluid-tight manner to the edge of the opening. The hydraulic fluid is introduced through the initially still open end of the narrow tube. After the filling with hydraulic fluid the open end of the narrow tube is sealed in fluid-tight manner, for example by squeezing. The narrow tube can serve at the same time a force-transmitting or travel-transmitting member which connects the diaphragm to a force or travel sensor.