On an inner wall surface of a plug hole, an internal thread portion and a seat portion are formed. The seat portion has a tapered seat surface. A glow plug with a combustion pressure sensor includes a housing, a glow heater, a load transfer member, and a pressure detector. The housing has an external thread and a seat facing portion. The seat facing portion has a tapered contact surface in surface contact with the tapered seat surface. A recessed portion recessed to be in non-contact with the seat portion is formed annularly about a central axis of the housing.