Spark plug

A spark plug, comprising:

• an insulator that extends along an axial line from a front end side of the spark plug to a rear end side of the spark plug;
• and
• a cylindrical metal shell that is disposed on an outer peripheral side of the insulator, the metal shell including a stepped portion at an inner periphery of the metal shell, the stepped portion protruding inward in a radial direction, the stepped portion comprising:
• a first convex portion that includes a rear-end-side facing surface, the rear-end-side facing surface facing the rear end side of the spark plug and retaining the insulator either directly or via another member;
• a second convex portion that is disposed adjacent to the first convex portion on a front end side of the first convex portion, the second convex portion including a front-end-side facing surface, the front-end-side facing surface facing the front end side of the spark plug, the front-end-side facing surface having a front end that is positioned at a rear end side of a front end surface of the metal shell and
• a connection portion that connects the first convex portion and the second convex portion to each other,
• wherein, when a cross section including the axial line is viewed, in a direction perpendicular to the axial line, the connection portion exists in a range where a portion of the rear-end-side facing surface that contacts the insulator or the other member is positioned, and
• wherein, in the cross section including the axial line, a length of the first convex portion on an imaginary straight line is less than a length of the second convex portion on the imaginary straight line, the imaginary straight line passing through the connection portion and extending along the axial line.