SPARK PLUG MANUFACTURING METHOD

An object is to provide a spark plug manufacturing method capable of providing a spark plug equipped with an insulator having dielectric strength by means of judging whether or not the insulator has a defect. The spark plug manufacturing method of the present invention is characterized by including a defect judgment step of judging whether or not the insulator has a defect, by means of generation of an electric potential difference between the center electrode and the metallic shell under conditions such that an assembly of the center electrode, the metallic shell, and the insulator is disposed within a pressure vessel, a high-pressure atmosphere higher in pressure than the atmospheric pressure is established within the pressure vessel, a space which allows the presence of insulating oil is a space surrounded by the packing, the metallic shell, the insulator, and an imaginary plane containing a forward end surface of the metallic shell, and the insulating oil is present at least in a region of the space where the distance between the ledge and the insulator becomes shortest.