Spark plug and manufacturing method thereof

A spark plug comprising:

• a center electrode extending in an axial line direction;
• a cylindrical insulator accommodating the center electrode therein such that a front end part of the center electrode is exposed out of a front end side of the insulator;
• a cylindrical metal shell accommodating the insulator therein;
• a front end member arranged in a front end part of the metal shell and having an opening opened in the axial line direction;
• and
• a weld portion that is formed along an outer circumference end part of the front end member and in which the front end member and the metal shell have been mutually melted, wherein
• the weld portion has a plurality of melt extending parts each extending toward an inner circumference side from the outer circumference end part of the front end member, and
• the plurality of melt extending parts are provided aligned along the outer circumference end part of the front end member such that adjacent melt extending parts are connected to each other in an outer-circumference-side end part, and partially include a smaller melt extending part in which a melting depth Dm is smaller than other melt extending parts, said depth Dm being a distance between a vertex of the melt extending part that is a furthest part from a surface of the weld portion and the surface of the weld portion.