diameter portion of the center electrode 3 is 2 3 mm the width g of the second ground electrodes 5 and 6 is 2 2 mm in this example the radius rofthe circle k is 0 05 mm the distance h of the wear resisting members 7 in the lengthwise direction of the spark plug 100 is 0 3 mm of the distance h the distance h1 between the base 3 c of the shoulder 3 b of the center electrode 3 and a lower end of the wear resisting members 7 leading to the large diameter portion of the center electrode 3 is 0 05 mm the distance h2 between the base 3 c of the shoulder 3 b and an upper end of the wear resisting members 7 lying on the shoulder 3 b is 0 25 mm the distance or depth t of the wear resisting members 7 in a radius direction of the spark plug 100 is 0 3 mm the width l of the wear resisting members 7 is 1 0 mm production process of the spark plug 100 especially formation of the wear resisting members 7 on the center electrode 3 will be described below in detail others are well known in the art and explanation thereof in detail will be omitted here the wear resisting members 7 may be formed by either of a pair.