A spark plug has an electrode including a base portion and a tip joined to a specific surface that is a specific outer surface of the base portion, the tip forming a spark discharge surface. Respective relative positions of a plurality of points on an outer surface of a target portion of the electrode including the base portion and the tip joined to the base portion, which is a portion including at least a portion of the specific surface of the base portion and the tip, are identified to generate three-dimensional coordinate data representing the three-dimensional shape of the target portion. The coordinate data is analyzed to determine whether the target portion of the electrode includes a predetermined unintentional portion that is an unintended portion. An electrode including the unintentional portion is excluded from objects to be manufactured, and an electrode not including the unintentional portion is used to assemble the spark plug.