Members as an upper fixing screw, piezoelectric element (15), a pressure transmitting member (14) are located closer to region of an engine to be measured and the like than a fitting thread portion of a sensor casing so that a pre-stress on the piezoelectric element can be constantly maintained at a predetermined value, thus enabling pressure measurement with a high degree of accuracy. Further, a projecting portion or a spacer is provided on the backside of a pressure receiving surface (13) in order to ensure the surface contact between the pressure transmitting member (14) and the back surface of the pressure receiving surface, thus preventing the stress from concentrating on corners of the bottom surface of the pressure transmitting member.