A combustion pressure sensor comprising: a tubular housing having an axial hole extending in a direction of an axis of the pressure sensor; a flexible member disposed within the axial hole and fixed at one end to the housing, the flexible member being displaceable and contractable along the direction of the axis; a rod-shaped pressure transmission body inserted into the axial hole and fixed, through its outer circumferential surface, to the other end of the flexible member, the pressure transmission body having a front end portion exposed to the outside; and a sensor element fixed directly or indirectly to the housing and outputting a signal on the basis of a pressure applied thereto from the pressure transmission body, wherein the housing has a screw portion for screw engagement with a mounting hole of an internal combustion engine, and a press contact portion which is press-contacted with the internal combustion engine when the screw portion is screwed into the mounting hole of the internal combustion engine, characterised in that, the one end of the flexible member is fixed to the housing on the front end side of a portion of the housing located at the center of the housing, between a rear end of the screw portion and the press contact portion; a region where the flexible member and the pressure transmission body are fixed together is located within the housing; and a relation A < B is satisfied where A represents an amount of compression of a portion of the housing between a portion of the housing to which the flexible member is fixed and a front end of the screw portion, and B represents an amount of compression of a portion of the housing between the portion of the housing to which the flexible member is fixed and a front end of the press contact portion, the compression amounts being measured when a force along the axis is applied to a portion of the housing located between the front end of the screw portion and the press contact portion. a tubular housing having an axial hole extending in a direction of an axis of the pressure sensor; a flexible member disposed within the axial hole and fixed at one end to the housing, the flexible member being displaceable and contractable along the direction of the axis; a rod-shaped pressure transmission body inserted into the axial hole and fixed, through its outer circumferential surface, to the other end of the flexible member, the pressure transmission body having a front end portion exposed to the outside; and a sensor element fixed directly or indirectly to the housing and outputting a signal on the basis of a pressure applied thereto from the pressure transmission body, wherein the housing has a screw portion for screw engagement with a mounting hole of an internal combustion engine, and a press contact portion which is press-contacted with the internal combustion engine when the screw portion is screwed into the mounting hole of the internal combustion engine, characterised in that, the one end of the flexible member is fixed to the housing on the front end side of a portion of the housing located at the center of the housing, between a rear end of the screw portion and the press contact portion; a region where the flexible member and the pressure transmission body are fixed together is located within the housing; and a relation A < B is satisfied where A represents an amount of compression of a portion of the housing between a portion of the housing to which the flexible member is fixed and a front end of the screw portion, and B represents an amount of compression of a portion of the housing between the portion of the housing to which the flexible member is fixed and a front end of the press contact portion, the compression amounts being measured when a force along the axis is applied to a portion of the housing located between the front end of the screw portion and the press contact portion.