A method of manufacturing a spark plug comprising: a center electrode extending in a direction of an axis; a tubular insulator provided around the center electrode; a tubular metallic shell provided around the insulator; a rodlike ground electrode joined to a front end portion of the metallic shell; and a tip joined to the ground electrode through a joining surface of the tip, the tip forming a gap between the tip and a front end portion of the center electrode, the method being characterized by comprising a tip forming step of forming the tip, and a tip joining step of resistance-welding the tip to the ground electrode, wherein the tip forming step includes: a wire rod forming step of forming a wire rod which is formed of the same metal as that of the tip, which has a rectangular cross section, and which has a reference surface on its side surface, and a wire rod cutting step of cutting the wire rod by moving a predetermined cutting blade from one edge of the reference surface with respect to a width direction thereof toward the other edge of the reference surface with respect to the width direction, to thereby obtain the tip, wherein in the tip joining step, at least a portion of the reference surface of the tip is joined to the ground electrode, whereby the portion of the reference surface becomes the joining surface. a center electrode extending in a direction of an axis; a tubular insulator provided around the center electrode; a tubular metallic shell provided around the insulator; a rodlike ground electrode joined to a front end portion of the metallic shell; and a tip joined to the ground electrode through a joining surface of the tip, the tip forming a gap between the tip and a front end portion of the center electrode, the method being characterized by comprising a tip forming step of forming the tip, and a tip joining step of resistance-welding the tip to the ground electrode, wherein the tip forming step includes: a wire rod forming step of forming a wire rod which is formed of the same metal as that of the tip, which has a rectangular cross section, and which has a reference surface on its side surface, and a wire rod cutting step of cutting the wire rod by moving a predetermined cutting blade from one edge of the reference surface with respect to a width direction thereof toward the other edge of the reference surface with respect to the width direction, to thereby obtain the tip, wherein in the tip joining step, at least a portion of the reference surface of the tip is joined to the ground electrode, whereby the portion of the reference surface becomes the joining surface. a wire rod forming step of forming a wire rod which is formed of the same metal as that of the tip, which has a rectangular cross section, and which has a reference surface on its side surface, and a wire rod cutting step of cutting the wire rod by moving a predetermined cutting blade from one edge of the reference surface with respect to a width direction thereof toward the other edge of the reference surface with respect to the width direction, to thereby obtain the tip, wherein in the tip joining step, at least a portion of the reference surface of the tip is joined to the ground electrode, whereby the portion of the reference surface becomes the joining surface.