A spark plug for an internal combustion engine comprising: a center electrode which has a bar shape extending in the direction of an axis; an insulator which has a substantially cylindrical shape and is provided on the outer periphery of the center electrode; a tubular metal shell which is provided on the outer periphery of the insulator; and a ground electrode which has a base end portion joined to the metal shell and a front end portion disposed to face a front end portion of the center electrode, wherein a ground electrode precious metal tip is joined to the front end portion of the ground electrode at a position opposed to the front end portion of the center electrode or a center electrode precious metal tip joined to the front end of the center electrode, wherein a spark discharge gap is formed between the front end portion of the center electrode or the front end portion of the center electrode precious metal tip, and the front end portion of the ground electrode precious metal tip, wherein the ground electrode precious metal tip is joined to a bearing surface of a mounting part containing the same component as the ground electrode with a fused part formed by performing laser welding or electron beam welding on the metal of the two to be fused together, wherein the mounting part is joined to the ground electrode, wherein the mounting part includes: a disc shape base part having one end surface which is joined to the ground electrode; a protruding part which protrudes from the other end surface of the base part and has a columnar shape with a smaller diameter than that of the base part, and to which the ground electrode precious metal tip is joined; and a part of the base part which protrudes in the outer peripheral direction from the protruding part is a flange part, and wherein grain size of the grains of the flange part is smaller than the grain size of the grains of the protruding part; characterised in that the grains of the flange part are flat and oriented in a direction perpendicular to the direction of the axis of the mounting part. a center electrode which has a bar shape extending in the direction of an axis; an insulator which has a substantially cylindrical shape and is provided on the outer periphery of the center electrode; a tubular metal shell which is provided on the outer periphery of the insulator; and a ground electrode which has a base end portion joined to the metal shell and a front end portion disposed to face a front end portion of the center electrode, wherein a ground electrode precious metal tip is joined to the front end portion of the ground electrode at a position opposed to the front end portion of the center electrode or a center electrode precious metal tip joined to the front end of the center electrode, wherein a spark discharge gap is formed between the front end portion of the center electrode or the front end portion of the center electrode precious metal tip, and the front end portion of the ground electrode precious metal tip, wherein the ground electrode precious metal tip is joined to a bearing surface of a mounting part containing the same component as the ground electrode with a fused part formed by performing laser welding or electron beam welding on the metal of the two to be fused together, wherein the mounting part is joined to the ground electrode, a disc shape base part having one end surface which is joined to the ground electrode; a protruding part which protrudes from the other end surface of the base part and has a columnar shape with a smaller diameter than that of the base part, and to which the ground electrode precious metal tip is joined; and a part of the base part which protrudes in the outer peripheral direction from the protruding part is a flange part, and wherein grain size of the grains of the flange part is smaller than the grain size of the grains of the protruding part; characterised in that the grains of the flange part are flat and oriented in a direction perpendicular to the direction of the axis of the mounting part.