The spark plug includes an insulator, a metal shell, and a buffering member. The buffering member is filled in a space that is enclosed by an inner peripheral surface of the metal shell and an outer peripheral surface of the insulator. 3 mm2≤L×T is satisfied in a case where: a length in a direction of an axial line of a filled portion filled with the buffering member is defined as a filling length L; a thickness, of a screw portion of the metal shell, that is half a difference left after subtraction of the inner diameter of the metal shell from the pitch diameter of the screw portion is defined as an effective thickness; and a minimum value of the effective thickness of a portion, of the screw portion, present rearward of an inner diameter reduction portion of the metal shell is defined as a minimum thickness T.