Abstract: A pressure switch includes a housing, the inner space of which is divided into a pressurized fluid operating chamber and a switch mechanism chamber by a flexible diaphragm. The operating chamber communicates with a pressurized fluid inlet hole, and the mechanism chamber houses a switch mechanism. The diaphragm is hermetically fixed to the inner surface of the housing by an elastic seal member. The switch mechanism has a spring for urging the diaphragm toward the operating chamber. The switch mechanism is turned on or off as the diaphragm is transformed against the urging force of the spring by the pressure of a fluid introduced through the inlet hole into the operating chamber. The diaphragm is constructed by stacking a metal film and a flexible plastic film in layers so that the films are independent of each other.