PURPOSE: To supply both a high voltage for sparking and electric power for a ceramic heater with only one plug cap by disposing a connector fitting for holding the plug terminal of a spark plug in a cord connecting portion.

CONSTITUTION: In a spark plug 300 with a heater, the rear end 320 of an insulator is surrounded with an exposed electrode 360. One end 351 of a ceramic heater 350 is electrically conducted to a main fitting 310, while the other end 352 thereof is electrically conducted to the exposed electrode 360. A plug cap P is of a double structure consisted of a cap main body 1 made of a hard synthetic resin and a coating layer 2 made of an electrical insulating silicone rubber having elasticity. A connector fitting 3 is embedded in the inner wall of the cap main body 1. A spring electrode 4 is disposed in the guide groove 15 of the cap main body 1. Therefore, it is possible to obtain the plug cap capable of supplying both a high voltage and electric power for the ceramic heater.