A method for manufacturing a spark plug, the spark plug includes: a cylindrical metal shell having a portion to be caulked and a tool-engaging portion that is to be attached on an engine; an insulator that is inserted into the metal shell and extends axially; and a caulking metallic mold, the method including caulking the portion to be caulked to be fixed to an outer circumferential face of the insulator with the caulking metallic mold, where in the caulking metallic mold includes a face, the face including a hard carbon film that includes an amorphous carbon phase, and the face is contact with or sliding to the portion to be caulked.