To provide a glow plug comprising a terminal portion capable of preventing the breakage of an axis and the increase of contact resistance on the terminal portion even when the stress caused by firing pressure from a combustion chamber and the stress caused by vibration or the like of an engine are applied to the terminal portion of a glow plug rear end portion in the glow plug where a ceramic heater and the axis are mechanically connected.

In the ceramic heater 30, its rear end portion and a tip portion of the rod-shaped axis 20 are connected by a ring member 21. The terminal portion formed on the rear end portion of the rod-shaped axis 20 is composed of a circular member 70 and the rear end portion of the axis 20 projecting from the circular member 70 to a rear end side. By applying the terminal portion constituted as mentioned above, the stress applied to the axis 20 in vibration can be reduced in comparison with a conventional terminal portion constituted by combining a pin terminal and the axis 20, thus the breakage of the axis 20 and the increase of contact resistance can be inhibited or reduced.