Spark plug

A spark plug comprising:

• a center electrode including a nose portion that extends from a front side to a rear side along an axial line, and a flange portion that projects to a radially outer side from a rear end of the nose portion;
• a cylindrical insulator in which a receiving portion supporting the flange portion is formed on an axial hole formed along the axial line, and a step portion having a diameter that increases from the front side toward the rear side is formed on an outer circumferential surface;
• and
• a cylindrical metal shell in which a shelf portion supporting the step portion via a packing is formed on an inner circumferential surface and which is disposed at the radially outer side of the insulator, wherein
• a front end portion of the insulator disposed on the front side with respect to a front end edge of a first contact surface that the packing contacts with, of the step portion, has a length L of less than or equal to 9 mm in an axial direction,
• the front end portion includes an annular groove opened to the front side and formed around the axial line,
• the groove has a width of greater than or equal to 0.2 mm in a radial direction, and
• in a cross section including the axial line, a value D/L obtained by dividing, by the length L, a creepage distance D, from a position P on a frontmost side of a region in which a clearance distance between an outer surface of the front end portion and the inner circumferential surface of the metal shell is less than or equal to 0.1 mm to a connection position between the outer surface of the front end portion and the axial hole, is greater than or equal to 1.1.