A method of manufacturing a spark plug wherein a tip having a burr-free surface is more reliably welded to a ground electrode, to thereby realize an excellent joint strength. The spark plug includes a center electrode, a ground electrode, and a ground-electrode-side tip joined to the ground electrode through its joining surface. The method of manufacturing includes a tip forming step and a tip joining step of resistance-welding the ground-electrode-side tip to the ground electrode. A wire rod having a reference surface is formed, and the wire rod is cut by moving a cutting blade from one edge of the reference surface with respect to the width direction thereof toward the other edge of the reference surface with respect to the width direction, thereby obtaining the ground-electrode-side tip. At least a portion of the reference surface is joined to the ground electrode, whereby that portion becomes the joining surface.