| 摘要 |
A ground electrode has one end portion fixed to a metal housing, a bent portion provided at an intermediate portion thereof, and the other end portion positioned in a confronting relationship with a center electrode to form a spark discharge gap. The ground electrode contains either Ni or Fe as a main component and at least one additive selected from the group consisting of Cr and Al. A cross-sectional area S of the ground electrode is not less than 2 mm<SUP>2 </SUP>and not greater than 3 mm<SUP>2</SUP>. An average value D of crystal grain diameters in a thickness direction is not less than 100 mum at least at the bent portion.
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