A glow plug having a rod-shaped heater including a resistance heating element; a tubular metallic shell; a rod-shaped inner shaft accommodated in the metallic shell and to which electric current is applied externally; and a conductive tubular member disposed inside the metallic shell. The tubular member has openings at its opposite ends. The rear end of the heater is press-fitted into one of the openings, and the front end portion of the inner shaft is inserted into the other opening, whereby the resistance heating element and the inner shaft are electrically connected. The heater includes an electrode terminal portion formed on the outer circumferential surface thereof. The tubular member includes an intermediate portion located between the one end and the other end and in contact with the electrode terminal portion, and the wall thickness at the one end is smaller than the wall thickness at the intermediate portion.