Disclosed is a spark plug including: an insulator having an axial hole formed along an axis of the spark plug; a center electrode disposed in a front end side of the axial hole; and a metal shell fixed around an outer circumference of the insulator, with a front end portion of the insulator protruding frontward from a front end of the metal shell. The front end portion of the insulator consists only of a first section and a second section located adjacent to and frontward of the first section and having an inner diameter larger than that of the first section. The second section has a chamfered area formed on an inner circumferential surface thereof so as to continue to a front end of the insulator.