Spark plug

A spark plug comprising:

• a tubular metal shell that extends from a front-end side toward a rear-end side along an axial line;
• a center electrode that is insulated and held on an inner peripheral side of the metal shell;
• a ground electrode that has one end portion joined to the metal shell and the other end portion forming a spark gap between the other end portion and a front end portion of the center electrode;
• and
• a cap member that is joined to a front end portion of the metal shell, that covers the front end portion of the center electrode and the other end portion of the ground electrode and forms a sub-chamber, and in which a through hole that connects the sub-chamber and a combustion chamber is formed,
• wherein a first fused portion that joins the metal shell and the cap member is located on the front-end side relative to the spark gap,
• wherein the spark plug includes a first facing portion at which the metal shell and the cap member face each other,
• wherein at least a part of the first facing portion is located on the sub-chamber side relative to the first fused portion, and
• wherein the first fused portion is not formed in an inner peripheral surface of the metal shell and an inner peripheral surface of the cap member.