Spark plug, and method for manufacturing spark plug

A spark plug comprising:

• an insulator having a axial hole penetrating in a direction of an axis;
• a central electrode provided on a front end side of the axial hole;
• a tubular metal shell that holds the insulator;
• and
• a ground electrode including a surface layer and a core material that is surrounded by the surface layer and has a larger thermal conductivity than that of the surface layer, wherein
• the metal shell has a protruding portion in which at least a part of the metal shell protrudes toward a front end side only in the direction of the axis,
• the core material prior to joining is exposed to an outside on a first end surface present at one end of the ground electrode in a longitudinal direction,
• the core material is not exposed to the outside on a second end surface present at an other end of the ground electrode in the longitudinal direction, and
• the first end surface of the ground electrode is joined to an inside surface of the protruding portion such that the first end surface is not exposed to the outside after joining to the inside surface, said inside surface facing the axis, and the other end portion of the ground electrode in the longitudinal direction faces the central electrode.