Spark plug

A spark plug comprising:

• a center electrode which extends in an axial direction;
• a cylindrical insulator which is disposed around an outer circumference of the center electrode;
• a cylindrical metal shell which is disposed around an outer circumference of the insulator;
• and
• a ground electrode having one end connected to the metal shell and which is curved from the one end to another end thereof, and
• an end surface of the other end being positioned between the one end and the center electrode or on the center electrode, when viewed in the axial direction of the center electrode,
• wherein the end surface has a maximum width portion which has a maximum width in a direction perpendicular to the axial direction of the center electrode,
• wherein the maximum width portion of the end surface is formed only at a position where a distance from a center position of the end surface is 12% to 88% of a distance from the center position of the end surface an outer side surface of the ground electrode in a direction directed from an inner side surface of the ground electrode to the outer side surface of the ground electrode, and
• wherein the more away from the maximum width portion toward the inner side surface and the outer side surface of the ground electrode, respectively, the more reduced the width of the end surface is in the direction perpendicular to the axial direction of the center electrode.