A spark plug having an insulator with a front end portion having an annular groove opened to a front side around an axial line. The groove has a width of greater than or equal to 0.2 mm in a radial direction. In a cross section including the axial line, a value D/L obtained by dividing, by a length L, a creepage distance D, from a position P on the frontmost side of a region in which a clearance distance between an outer surface of a front end portion and an inner circumferential surface of a metal shell is less than or equal to 0.1 mm to a connection position between an outer surface of the front end portion and the axial hole, is greater than or equal to 1.1.