When a combustion pressure sensor (5, 5A...) is formed that includes at least: a case member (31...) which has a joint surface (31a...) on the side of a tip end and in which an opening portion is provided; a joint surface (41a...) which is brought into planar contact with the joint surface (31a...) of the case member (31...) so as to block the opening portion; a pressure reception member (40 ...) on which a combustion pressure acts; a welding portion (J2...) in which the joint surfaces (31a and 41a...) are joined to each other; and a piezoelectric element (10...) which is stored in the case member (31 ...) and converts a pressing force based on the combustion pressure transmitted from the pressure reception member (40...) into a signal, on the side of one edge side in at least the one joint surface (41a...), the one joint surface (41a...) is limited to a given depth of welding (t...) from the other edge side, a predetermined clearance portion (90...) is provided so as to form a predetermined gap with the opposite other joint surface (31a...) and a welding portion (J2...) is provided which includes at least all the limited joint surface (41a...) from the other edge side in the one joint surface (41a...).