A spark plug (1; 101; 102) comprising: a rod-shaped center electrode extending in an axis direction of the spark plug; a cylindrical insulator having an axial hole formed therein in the axis direction and retaining the center electrode in the axial hole; a cylindrical metal shell disposed on an outer circumference of the insulator; and a ground electrode (27; 47; 48) made of a nickel-based alloy, extending from a front end portion of the metal shell and bent at a substantially middle portion thereof in such a manner as to define a spark gap between a front end portion of the ground electrode (27; 47; 48) and a front end portion of the center electrode, characterized in that: the spark plug (1; 101; 102) further comprises: a molten layer in which a metal material of a nickel-based plating film applied to at least a center-electrode-side part of the portion of the ground electrode to be bent and a metal material of the ground electrode (27; 47; 48) are molten together by irradiation with a laser beam or electron beam on the center-electrode-side part of the portion of the ground electrode to be bent; and a nickel-based plating layer on a part of the ground electrode (27; 47; 48) other than the part irradiated with the laser light or electron beam, wherein a maximum length (Dp) between a point of a surface of the plating layer closest to the molten layer and a point of the molten layer opposite from the surface of the plating layer in a thickness direction of the ground electrode (27; 47; 48) is larger than or equal to a thickness of the plating layer, and the maximum length (Dp) between the point of the surface of the plating layer closest to the molten layer and the point of the molten layer opposite from the surface of the plating layer in the thickness direction of the ground electrode (27; 47; 48) is 200 μm or smaller. a rod-shaped center electrode extending in an axis direction of the spark plug; a cylindrical insulator having an axial hole formed therein in the axis direction and retaining the center electrode in the axial hole; a cylindrical metal shell disposed on an outer circumference of the insulator; and a ground electrode (27; 47; 48) made of a nickel-based alloy, extending from a front end portion of the metal shell and bent at a substantially middle portion thereof in such a manner as to define a spark gap between a front end portion of the ground electrode (27; 47; 48) and a front end portion of the center electrode, characterized in that: the spark plug (1; 101; 102) further comprises: a molten layer in which a metal material of a nickel-based plating film applied to at least a center-electrode-side part of the portion of the ground electrode to be bent and a metal material of the ground electrode (27; 47; 48) are molten together by irradiation with a laser beam or electron beam on the center-electrode-side part of the portion of the ground electrode to be bent; and a nickel-based plating layer on a part of the ground electrode (27; 47; 48) other than the part irradiated with the laser light or electron beam, wherein a maximum length (Dp) between a point of a surface of the plating layer closest to the molten layer and a point of the molten layer opposite from the surface of the plating layer in a thickness direction of the ground electrode (27; 47; 48) is larger than or equal to a thickness of the plating layer, and the maximum length (Dp) between the point of the surface of the plating layer closest to the molten layer and the point of the molten layer opposite from the surface of the plating layer in the thickness direction of the ground electrode (27; 47; 48) is 200 μm or smaller.