| 摘要 |
To improve the accuracy of a judgment as to whether or not a discharge penetrating an insulator has occurred. A spark plug which includes a center electrode extending in an axial direction, an insulator having an axial hole which extends in the axial direction and in which the center electrode is disposed, a metallic shell disposed around the insulator, and a ground electrode electrically connected to the metallic shell and forming a gap in cooperation with the center electrode is manufactured by the following method. An assembly is formed by combining the metallic shell, the insulator, and the center electrode. A voltage is applied between the metallic shell and the center electrode of the assembly. In a period during which the voltage is applied, a judgment as to whether or not a discharge penetrating the insulator has occurred is made by using an output value output from an optical sensor directed toward a forward end portion of the assembly. |
