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.