Spark plug

A spark plug comprising:

• a center electrode;
• a metallic member provided to form a tubular shape around an axis of the spark plug and holding the center electrode therein in an insulated state, the metallic member having a hole formed in a side wall of the metallic member and extending in a radial direction;
• and
• a ground electrode supported in the hole and extending from the hole toward the axis,
• wherein the ground electrode has a fixing portion formed of a metal and fixed to the hole, and an ignition portion containing a noble metal, disposed on a side toward the axis in relation to the fixing portion, and having a discharge surface for forming a gap between the ignition portion and the center electrode,
• wherein an absolute value of a difference in coefficient of thermal expansion between the metallic member and the fixing portion is smaller than an absolute value of a difference in coefficient of thermal expansion between the metalli's c member and the ignition portion,
• wherein the ground electrode has the fixing portion, the ignition portion, and a connecting portion for connecting together the fixing portion and the ignition portion, and
• wherein a cross-sectional area of the ground electrode at a boundary between the fixing portion and the connecting portion, as measured parallel to the axis and perpendicularly to an extension direction in which the ground electrode extends, is larger than a cross-sectional area of the ground electrode at an end portion of the connecting portion on a side toward the ignition portion, as measured parallel to the axis and perpendicularly to the extension direction of the around electrode.