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 has a length L of less than or equal to 9 mm in an axial direction from a front end edge to a front end surface of the insulator , wherein the front end edge is an edge present on the frontmost side of a first contact surface of the step portion that the packing contacts with the first contact surface ; 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. 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 has a length L of less than or equal to 9 mm in an axial direction from a front end edge to a front end surface of the insulator , wherein the front end edge is an edge present on the frontmost side of a first contact surface of the step portion that the packing contacts with the first contact surface ; 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. <EOS>