PURPOSE: To aim at improvement in a flashover generating voltage without any necessity for changing the position of a ceramic heater by setting the maximum diameter of a discharge portion at 0.3-1.0mm.

CONSTITUTION: In a spark plug A with a heater, an electrode chip 2 and a central shaft (central electrode) 3 are inserted into the shaft hole 11 of an insulator 1, and a ceramic heater 4 is integrally formed in the groove 13 of a leg portion 12. The heater 4 is a heat generating pattern 42 formed at the inner circumference of an alumina sintering body (ceramic insulated coating layer) 41. The electrode chip 2 made of platinum alloy is consisted of a flange-type front end portion and a rear end portion 21 having a small diameter, where the front end portion serves as a discharge portion 22 projecting from the insulator 1. In this case, the maximum diameter of the discharge portion in the central electrode 3 is 0.3-1.0mm, and the thickness of the ceramic insulated coating layer 41 is 0.1mm or more. Therefore, it is unnecessary to change the position of the heater 4 so as to aim at improvement in a flashover generating voltage.