A spark plug, comprising: an insulator that extends along a central axis (CO), the insulator including a through hole that passes through the insulator along the central axis (CO); a center electrode that extends along the central axis (CO), the center electrode including a rear end positioned inside of the through hole ; a metal terminal nut that extends along the central axis (CO), the metal terminal nut including a tip end positioned at the rear end side with respect to the rear end of the center electrode inside of the through hole ; a resistor disposed in a position between the center electrode and the metal terminal nut inside of the through hole and apart from the center electrode ; and a conductive seal disposed between the resistor and the center electrode inside of the through hole , the conductive seal contacting both the center electrode and the resistor , the conductive seal includes a glass and metal; wherein the resistor has a contact surface in contact with the conductive seal , the contact surface including: a first and a second contact position (PP1, PP2) with an inner peripheral surface of the insulator ; a portion where a distance in the central axis (CO) direction between the contact surface and a virtual plane changes according to a position on the contact surface , the virtual plane including a rear end of the resistor and being perpendicular to the central axis (CO); and at least one point where the distance is a local maximum (SP1, SP2, SP4, SP5, SP7, SP8) and at least one point where the distance is a local minimum (BP1, SP6, SP9), in at least one cross section including the central axis (CO). an insulator that extends along a central axis (CO), the insulator including a through hole that passes through the insulator along the central axis (CO); a center electrode that extends along the central axis (CO), the center electrode including a rear end positioned inside of the through hole ; a metal terminal nut that extends along the central axis (CO), the metal terminal nut including a tip end positioned at the rear end side with respect to the rear end of the center electrode inside of the through hole ; a resistor disposed in a position between the center electrode and the metal terminal nut inside of the through hole and apart from the center electrode ; and a conductive seal disposed between the resistor and the center electrode inside of the through hole , the conductive seal contacting both the center electrode and the resistor , the conductive seal includes a glass and metal; wherein the resistor has a contact surface in contact with the conductive seal , the contact surface including: a first and a second contact position (PP1, PP2) with an inner peripheral surface of the insulator ; a portion where a distance in the central axis (CO) direction between the contact surface and a virtual plane changes according to a position on the contact surface , the virtual plane including a rear end of the resistor and being perpendicular to the central axis (CO); and at least one point where the distance is a local maximum (SP1, SP2, SP4, SP5, SP7, SP8) and at least one point where the distance is a local minimum (BP1, SP6, SP9), in at least one cross section including the central axis (CO). <EOS>