In a spark plug (100), the resistor composition constituting a resistor (15) contains semiconductive ceramic particles, offering a superior load life characteristic. Also, the value of (.alpha.2-.alpha.1)/.alpha.1 >=-0.30, where a value of electric resistance between a terminal (13) and a center electrode (3) is .alpha.1 at 20.degree. C. and .alpha.2 at 150.degree. C., so that deterioration of the radio frequency noise prevention performance at high temperatures can be effectively suppressed. The resistor composition contains semiconductive ceramic particles whose temperature coefficient of electric resistance shows a positive value, or a negative value of relatively small absolute value, (e.g., TiO.sub.2 particles having a rutile type crystalline structure, titanate or zirconate of alkali earth metal elements, titanium suboxide, etc.), or titanium metal. Thus, the invention provides a resistor-incorporated spark plug which is enabled to offer a stable load life characteristic even when a high load acts thereon, and which is unlikely to deteriorate in the radio frequency noise prevention performance even under high temperatures.