Spark plug

A spark plug comprising:

• a center electrode extending in a direction of an axial line;
• a tubular metallic shell which holds the center electrode in an insulated condition and which has a penetration hole penetrating the metallic shell in a thickness direction;
• and
• a ground electrode which extends in a direction intersecting the direction of the axial line and which has a first end portion held in the penetration hole, and a second end portion located on a forward end side of the center electrode in the direction of the axial line such that a spark gap is provided between the second end portion and a forward end surface of the center electrode, wherein
• the penetration hole includes a circular counterbore portion provided on an outer circumferential side of the metallic shell, and a penetrating portion extending from the counterbore portion to an inner circumferential surface of the metallic shell;
• the ground electrode includes a circular plate-shaped fixing portion which is fixed to the counterbore portion, and an extension portion extending from one surface of the fixing portion to a position which faces the forward end surface of the center electrode in the direction of the axial line;
• a flat surface which faces the forward end surface of the center electrode in the direction of the axial line is provided on a side surface of the extension portion;
• and
• the penetrating portion restricts the extension portion such that the flat surface of the extension portion faces toward a rear end side in the direction of the axial line.