| 摘要 |
A buried portion (32B) buried from a junction target surface of a ground electrode (27) is provided in a noble metal tip (32). In a section, perpendicular to a central axis CL2 of the ground electrode (27), a large width portion (32W) is formed in the buried portion (32B), and a region between the junction target surface and a largest width region of the large width portion (32W) is formed into a shape which gradually increases in width, or into a shape having a region of the relevant shape and a constant width region. A region from the large width portion (32W) to a point of intersection P1, P2 is covered with a base material of the ground electrode (27) and a melt portion (35), and a thickness t1 (mm) of the noble metal tip (32) and a buried amount t2 (mm) satisfy 0.25≰t2/t1.
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