A spark plug includes an insulator; a center electrode; a metallic shell; a ground electrode disposed at a forward end portion of the metallic shell and forming a gap in cooperation with a forward end portion of the center electrode; and a tip at least a portion of which is joined to at least the one of two side surfaces of the ground electrode which is disposed downstream with respect to fuel gas flow. In a first imaginary plane which contains a forward end surface of the center electrode and on which a discharge surface of the tip is projected, at least a portion of a projected image of the discharge surface is located within a range of 2.5G from the outer circumference of the forward end surface of the center electrode, where G (mm) is the size of the gap.