A glow plug including a metal sheath tube having a closed front end; a heating element accommodated within the sheath tube; insulating powder filling the interior of the sheath tube so as to surround the heating element; a rod-shaped metal lead connected to the heating element and inserted into the sheath tube from the rear end thereof; and a seal member located in a seal portion at the rear end of the sheath tube to hermetically seal the gap between the sheath tube and the lead. The glow plug is characterized in that the sheath tube is formed to have a substantially uniform outer diameter over an axial range including and extending beyond a range where the seal portion is formed, and the sheath tube has an engagement projection formed at the seal portion and deformed so as to protrude radially inwardly.
