A spark plug is composed of a main metal fitting having a cylindrical structure, an insulator disposed inside the cylindrical main metal fitting, a center electrode fitted in the insulator in a manner that a front end portion of the center electrode projects outward over one end of the insulator, and a grounding electrode mounted to the main metal fitting and having one end portion opposing to the front end portion of the center electrode through a discharge gap therebetween. The front end portion of the center electrode includes a conical portion having a tapered surface having a taper angle of less than 80°, and a columnar portion formed to a top end portion of the conical portion so as to have a diameter in a range of 0.4 mm to 0.8 mm.