A combustion pressure sensor (1) includes a housing (2) having an axial hole (23), a flexible member (8) fixed at one end to the housing (2) and being displaceable along the direction of axis (CL1), a pressure transmission body (3) whose outer circumferential surface is fixed to the other end of the flexible member (8), and a sensor element (42) fixed to the housing (2) and outputting a signal on the basis of a pressure applied thereto from the pressure transmission body (3). The housing (2) includes a main body portion (21) having a screw portion (24), and a cap member (22) having a press contact portion (26) which is pressed against the internal combustion engine when the screw portion (24) is screwed into the mounting hole of an internal combustion engine. The one end of the flexible member (8) is fixed to the main body portion (21).