Method of manufacturing spark plug

A method of manufacturing a spark plug including a cylindrical tubular metallic shell having a screw portion on an outer surface thereof and a ground electrode attached to an end surface at one end of the metallic shell in the direction of the center axis thereof comprises a measurement step of measuring a surface of the screw portion which passes through a measurement region located at a predetermined position in the direction of the center axis, while rotating the metallic shell about the center axis thereof; an attachment position calculation step of calculating, on the basis of information obtained in the measurement step, an attachment position at which the ground electrode is attached to the end surface; and a joining step of joining the ground electrode to the end surface at the attachment position, wherein the measurement step includes a step of measuring a displacement of the surface of the screw portion by using a non-contact-type displacement sensor.