Patent ID: 6881930

Claim:
A glow plug comprising: a ceramic heater assuming a rodlike form and having a resistance-heating element embedded in a distal end portion thereof; a first metallic fitting member externally joined to a rear end portion of the ceramic heater in such a manner as to surround an outer circumferential surface of the rear end portion; a second metallic fitting member disposed on a side toward a distal end of the ceramic heater in relation to the first metallic fitting member and externally joined to the ceramic heater in such a manner as to surround an outer circumferential surface of the ceramic heater; and a pair of electric conductors embedded in the ceramic heater so as to electrically connect the resistance-heating element and the first and second metallic fitting members, one electric conductor having a first exposed portion joined to the first metallic fitting member, and the other electric conductor having a second exposed portion joined to the second metallic fitting member, wherein a metal layer not higher than Ni in ionization tendency is formed on an inner circumferential surface of the first metallic fitting member and on an inner circumferential surface of the second metallic fitting member, the inner circumferential surfaces facing the first and second exposed portions, respectively; and the metal layers are in contact with the corresponding first and second exposed portions.