To make highly reliable pressure measurements by preventing the deformation of a pressure receiving element even if the mounted condition of a base varies depending on the tightened conditions of bolts or vibration, etc.

In a sensor for measuring pressures, an FBG15a is fixed to a diaphragm 10a serving as a pressure receiving element, and the distortion of the diaphragm 10 is detected by the FBG15a so that the sensor measures the pressure applied to the diaphragm 10a The diaphragm 10a, the base 10b, and a collar part 10c provided on the outer edge of the base are formed integrally with each other and the collar part 10c is fixed to a case 11 by means of the bolts 14.