A spark plug has a metal shell and a cylindrical ceramic insulator disposed in an inner circumference of the metal shell. An axial hole extends in an axial line CL direction through the insulator, and has a tip located more to a tip side of the spark plug than a tip of the metal shell, and a distance along the axial line CL1 from the tip of the metal shell to the tip of the ceramic insulator is 0.5 mm or more. The insulator satisfies C ≧1.07 mm and V ≦3.9 mm3, where C is a thickness of the insulator in a cross section passing an inner circumference surface tip of the metal shell and orthogonal to the axial line CL1 ,and V is a volume of the ceramic insulator within a range of 0.5 mm from the tip of the ceramic insulator to a rear end side in the axial line CL1 direction.