A spark plug (1, 1A, 1B) comprising: a rod-shaped center electrode extending in an axial direction; an insulating body provided around an outer circumference of the center electrode; a metal shell provided around an outer circumference of the insulating body; a ground electrode (27, 37, 47) extending from a distal end portion of the metal shell; and a noble metal tip (31, 42, 52) joined to a distal end portion of the center electrode, and forming a gap between the ground electrode (27, 37, 47) and the noble metal tip (31, 42, 52), wherein the center electrode and the noble metal tip (31, 42, 52) are joined to each other through a molten portion (35, 46, 56) which is fused with a component of the center electrode and a component of the noble metal tip (31, 42, 52); an area of an interface (Bo) between the noble metal tip (31, 42, 52) and the center electrode is set to be 5% or less with respect to a cross-sectional area of the noble metal tip (31, 42, 52) which is perpendicular to an axial line at a portion, which is nearest to the molten portion (35, 46, 56), of an outer surface of the noble metal tip (31, 42, 52); in the cross section including the axial line, supposing that a length of a portion, which is exposed to the outer surface is A (mm), of the molten portion (35, 46, 56) along the axial line, and a width of the noble metal tip (31, 42, 52) is B (mm), A ≤ 0.6 and B/A ≤ 6 are satisfied; characterized in that the portion of the molten portion (35, 46, 56), of which a length along the axial line is A/1.5, is located further outwards radially than a position which comes in by as much as B/4 from the outer circumference of the noble metal tip (31, 42, 52). a rod-shaped center electrode extending in an axial direction; an insulating body provided around an outer circumference of the center electrode; a metal shell provided around an outer circumference of the insulating body; a ground electrode (27, 37, 47) extending from a distal end portion of the metal shell; and a noble metal tip (31, 42, 52) joined to a distal end portion of the center electrode, and forming a gap between the ground electrode (27, 37, 47) and the noble metal tip (31, 42, 52), wherein the center electrode and the noble metal tip (31, 42, 52) are joined to each other through a molten portion (35, 46, 56) which is fused with a component of the center electrode and a component of the noble metal tip (31, 42, 52); an area of an interface (Bo) between the noble metal tip (31, 42, 52) and the center electrode is set to be 5% or less with respect to a cross-sectional area of the noble metal tip (31, 42, 52) which is perpendicular to an axial line at a portion, which is nearest to the molten portion (35, 46, 56), of an outer surface of the noble metal tip (31, 42, 52); in the cross section including the axial line, supposing that a length of a portion, which is exposed to the outer surface is A (mm), of the molten portion (35, 46, 56) along the axial line, and a width of the noble metal tip (31, 42, 52) is B (mm), A ≤ 0.6 and B/A ≤ 6 are satisfied; characterized in that the portion of the molten portion (35, 46, 56), of which a length along the axial line is A/1.5, is located further outwards radially than a position which comes in by as much as B/4 from the outer circumference of the noble metal tip (31, 42, 52).