Abstract: According to the present invention, there is provided a pressure sensor unit (1) having a ring-like pressure sensing element (3), which is formed separately from a spark plug, in the state where a spark plug (100) has been attached a rear end of at least one of an inner cylinder member (6) and an outer cylinder member (5) in the direction of an axis (O) is located between the rear end of the pressure sensing element (3) and the rear end of a insulator (110) of the spark plug (standard section (SS)), while at the rear of the standard section (SS), no component of the pressure sensor unit (1) exists in an area inside the inner circumferential surface of the outer cylinder member (5) or its extended plate (EP).

Abstract: An object of the present invention is to provide a pressure sensor unit which is formed separately from a spark plug, and in which an extra space does not have to be secured in the peripheral portion of a pressure sensing element, while a space for attaching peripheral components such as an ignition coil and the like can be secured flexibly in a spark plug hole.