A method of manufacturing a spark plug which comprises: an insulator having an axial hole extending therethrough in an axial direction; a center electrode provided at a front end portion of the axial hole, a tubular metallic shell which holds the insulator; a ground electrode whose one end portion is attached to a front end portion of the metallic shell and whose other end portion faces a front end portion of the center electrode; a noble metal tip provided on a surface of the ground electrode which faces the front end portion of the center electrode, and having a discharge surface which forms a spark discharge gap in cooperation with the center electrode; and a fusion-zone at a boundary between the ground electrode and the noble metal tip, the fusion zone being configured such that when the fusion zone is projected in a direction perpendicular to the discharge surface, 80% or more of an area of an overlap between the ground electrode and the noble metal tip (an area S of an X region) overlaps the projected fusion zone and such that a shape of the fusion zone as viewed from a direction perpendicular to the discharge surface is symmetrical with respect to a centerline perpendicular to a width direction of the ground electrode and passing through a center of the noble metal tip, wherein the method comprises a fusion-zone formation step of forming the fusion zone through radiation of a high-energy beam to the boundary between the ground electrode and the noble metal tip, wherein the fusion-zone formation step includes a step of radiating the high-energy beam from a direction parallel to a plane which contains the boundary, and wherein the fusion-zone formation step includes a step of radiating the high-energy beam to the boundary while reciprocally moving the high-energy beam relative to the boundary and radiating the high-energy beam twice or more to a portion of the boundary, thereby rendering the shape of the fusion zone symmetrical with respect to the centerline. an insulator having an axial hole extending therethrough in an axial direction; a center electrode provided at a front end portion of the axial hole, a tubular metallic shell which holds the insulator; a ground electrode whose one end portion is attached to a front end portion of the metallic shell and whose other end portion faces a front end portion of the center electrode; a noble metal tip provided on a surface of the ground electrode which faces the front end portion of the center electrode, and having a discharge surface which forms a spark discharge gap in cooperation with the center electrode; and a fusion-zone at a boundary between the ground electrode and the noble metal tip, the fusion zone being configured such that when the fusion zone is projected in a direction perpendicular to the discharge surface, 80% or more of an area of an overlap between the ground electrode and the noble metal tip (an area S of an X region) overlaps the projected fusion zone and such that a shape of the fusion zone as viewed from a direction perpendicular to the discharge surface is symmetrical with respect to a centerline perpendicular to a width direction of the ground electrode and passing through a center of the noble metal tip, wherein the method comprises a fusion-zone formation step of forming the fusion zone through radiation of a high-energy beam to the boundary between the ground electrode and the noble metal tip, wherein the fusion-zone formation step includes a step of radiating the high-energy beam from a direction parallel to a plane which contains the boundary, and wherein the fusion-zone formation step includes a step of radiating the high-energy beam to the boundary while reciprocally moving the high-energy beam relative to the boundary and radiating the high-energy beam twice or more to a portion of the boundary, thereby rendering the shape of the fusion zone symmetrical with respect to the centerline.