A pressure sensor chip includes a sensor diaphragm, and first and second retaining members. The first and second retaining members face and are bonded to peripheral edge portions of a first face and another face of the sensor diaphragm, and have pressure guiding holes that guide measurement pressures to the sensor diaphragm. The first retaining member has, in an interior thereof, a non-bonded region that is continuous with a peripheral portion of the pressure guiding hole. The non-bonded region in the interior of the first retaining member is provided at a portion of a plane that is parallel to a pressure bearing surface of the sensor diaphragm. The second retaining member is provided with a recessed portion that prevents excessive dislocation of the sensor diaphragm when an excessively large pressure is applied to the sensor diaphragm.