Spark plug for internal combustion engine

A spark plug for an internal combustion engine comprising:

• a hollow cylindrical housing;
• a hollow cylindrical porcelain insulator which is retained inside the housing;
• a center electrode which is retained inside the porcelain insulator with a top portion thereof protruding outside the porcelain insulator;
• and
• a ground electrode which defines a spark gap between itself and the center electrode,
• wherein the ground electrode includes an upright portion which extends from a front end of the housing to a front side of the spark plug and an extension which is bent from the upright portion inwardly in a radial direction of the spark plug,
• wherein if a direction which is oriented perpendicular both to an extension lengthwise direction that is a lengthwise direction of the extension and to a plug axial direction that is an axial direction of the spark plug is defined as a lateral direction, and sides opposed to each other in the lateral direction are defined as a Y1 side and a Y2 side, respectively, the extension has an inner slant portion which faces the center electrode and is inclined away from the center electrode from the Y1 side to the Y2 side,
• wherein the extension has a first and a second edge which are opposed to each other in the lateral direction, and the inner slant portion continuously extends from the first edge to the second edge of the extension, and
• wherein when viewed in the extension lengthwise direction, a center of the inner extension surface in the lateral direction is offset to the Y2 side from a center of a front end surface of the center electrode in the lateral direction.