Disclosed is a method for manufacturing a spark plug in which a tip is welded to a ground electrode. After the tip is welded to a distal end portion of the ground electrode, polishing treatment or grinding treatment is performed on at least a part of an edge region of a distal end face of the ground electrode. After the polishing or grinding treatment, an image of the distal end face of the ground electrode and the tip is taken with the use of reflected light and then analyzed by image processing.