PURPOSE: To increase the oxidation resistance of a glow plug having a sheath heater projected outwardly from an end of shaft bore defined in a main body thereof, the sheath heater being filled with a highly heat conductive insulation powder, and a heating coil contained in a metal tube thereof, by forming the heating coil and the powder with a special material.

CONSTITUTION: A sheath heater 1 comprises a heating coil 12 having its one end 12a connected with an inner base surface of metal tube 11, and a central shaft 13a of central electrode 13 connected with and projected upwardly from other end 12b of the heating coil 12, these heating coil and the central shaft being housed inside the sheath heater 1. The sheath heater is internally filled with a highly heat conductive insulation powder 14. The sheath heater has an outer periphery of heating coil formed as a heating section 1a and projected outwardly therefrom for being brazed with the end of shaft bore 2a of the main body fitting 2. In this case, a thin wire made of tungsten or molybdenum is employed as a material of heating coil 12, and the insulation powder 14 is composed by a compound of alumina and nitride, especially nitride silica, nitride aluminum or nitride boron.