Patent ID: 8188640

Claim:
A spark plug comprising: a center electrode having a tip end portion, a bulging flange portion which is disposed on a rear end side with respect to said tip end portion, and which has a larger diameter than said tip end portion, and a columnar middle trunk portion which is disposed between said tip end portion and said flange portion; an insulator which covers an outer circumference of said center electrode; a tubular metal shell which covers an outer circumference of said insulator; and a ground electrode which is joined to a tip end face of said metal shell, and which is placed so that one end of itself is opposed to said tip end portion of said center electrode, wherein said center electrode includes a core portion and a cover portion which covers said core portion, a ratio of a thickness of said cover portion of said middle trunk portion to a thickness of said cover portion of said flange portion is 0.8 or less, and the core portion is provided in at least the columnar middle trunk portion and the bulging flange portion.