| 摘要 |
PROBLEM TO BE SOLVED: To facilitate implementation of appropriate attachment of a noble metal tip.SOLUTION: A ground electrode is used, the ground electrode including a noble metal tip, a holding part having a through hole in which the noble metal tip is disposed, and a body part to which the holding part is joined. When a forward end side is a side toward the gap as viewed from the noble metal tip, an inside diameter Gf represents an inside diameter of the holding part at a forward end surface of the holding part, an inside diameter Gr represents an inside diameter of the holding part at a rearward end surface of the holding part, an outside diameter Tf represents an outside diameter of the noble metal tip at a forward end surface of the noble metal tip, and an outside diameter Tr represents an outside diameter of the noble metal tip at a rearward end surface of the noble metal tip, the inside diameter Gf is less than the outside diameter Tr, the inside diameter Gf is less than the inside diameter Gr, and the outside diameter Tf is less than the outside diameter Tr. At least one of the inner circumferential surface of the holding part which forms the through hole, and the outer circumferential surface of the noble metal tip at a portion which is disposed in the through hole continuously reduces in diameter toward the forward end side. The forward end surface of the noble metal tip is located on the forward end side with respect to the forward end surface of the holding part. |
