An object is to provide a glow plug in which a gap can be prevented from being generated between a ceramic heater and a cylindrical member even at the time of use in an internal combustion engine, etc. so that electrical conduction of the glow plug can be prevented from being lowered. A glow plug includes: a rod-shaped ceramic heater 2; a rod-shaped center pole 5 extending axially so as to electrically connect to the outside; and a cylindrical member 100 having a front end portion 101 bonded to an outer circumferential surface 2a of a rear end side of the ceramic heater 2, and a rear end portion 102 bonded to an outer circumferential surface of a front end side of the center pole 5, the cylindrical member 100 being made by a metal material for electrically connecting one of a pair of lead portions and the center pole 5 to each other, the glow plug characterized in that the cylindrical member 100 has a Vickers hardness of not lower than 200 HV at 25.degree. C.