To provide a glow plug preventing cracking of a heater by reducing pressing force acting on the heat in press fitting.

This glow plug 1 has: a cylindrical housing 2 having an outer peripheral screw section engaged with a plug mounting hole 80 on its outer peripheral face 20; a sleeve 3 having an expanded section 31 of which an outer diameter is expanded at a basic end side; and the heater 4 inserted into a combustion chamber 81 of an internal combustion engine 8 in a state that its tip section is projected from a tip side of the sleeve 3. The housing 2 and the sleeve 3 are connected by press fitting a press fitting section 62 formed on one of a tip section of the housing 2 and a basic end section of the expanded section 31, into a press-fitted section 61 composed of the other one. A clearance 5 where the press fitting section 62 and the heater 4 are not kept into contact with each other, is formed at least partially between the press fitting section 62 and the heater 4, in a projection region where a contact part of the press-fitted section 61 and the press fitting section 62 is projected toward the heater 4 on a radial inner side.