A spark plug comprising: a center electrode extending in a direction of an axis; a ceramic insulator having an axial bore extending in the direction of the axis and holding the center electrode in the axial bore; a metallic shell provided externally of an outer circumference of the ceramic insulator; and a ground electrode having an extending portion extending in the direction of the axis, attached to the metallic shell at one end, and forming, at the other end, a gap in cooperation with the center electrode, wherein at least one of the center electrode and the ground electrode has an electrode base metal (21, 31), a columnar noble metal tip (28, 38) disposed in such a manner as to face the other electrode, and an intermediate member (26, 36) disposed between the electrode base metal (21, 31) and the noble metal tip (28, 38); the intermediate member (26, 36) has a first surface (26f1, 36f1) in contact with the noble metal tip (28, 38) and a second surface (26f2, 36f2) being in contact with the electrode base metal (21, 31), located opposite the first surface (26f1, 36f1), and having an area greater than that of a cross section of the noble metal tip (28, 38) cut by a plane parallel to the first surface (26f1, 36f1); and a nugget is formed through fusion and solidification resulting from welding at at least a portion of a boundary between the intermediate member (26, 36) and the electrode base metal (21, 31); the spark plug being characterized in that in a section of the spark plug cut by a plane which passes through the center of gravity of the intermediate member (26, 36) and is in parallel with a facing direction between the extending portion and the center electrode, a relational expression S1/(D1 × H1) ≥ 0.005 is satisfied, where S1 is a total area of the nugget, H1 is a height of an end surface of the noble metal tip (28, 38) from a disposition surface (21f, 31bf) of the electrode base metal (21, 31) where the intermediate member (26, 36) is disposed, and D1 is a maximum width of the noble metal tip (28, 38). a center electrode extending in a direction of an axis; a ceramic insulator having an axial bore extending in the direction of the axis and holding the center electrode in the axial bore; a metallic shell provided externally of an outer circumference of the ceramic insulator; and a ground electrode having an extending portion extending in the direction of the axis, attached to the metallic shell at one end, and forming, at the other end, a gap in cooperation with the center electrode, wherein at least one of the center electrode and the ground electrode has an electrode base metal (21, 31), a columnar noble metal tip (28, 38) disposed in such a manner as to face the other electrode, and an intermediate member (26, 36) disposed between the electrode base metal (21, 31) and the noble metal tip (28, 38); the intermediate member (26, 36) has a first surface (26f1, 36f1) in contact with the noble metal tip (28, 38) and a second surface (26f2, 36f2) being in contact with the electrode base metal (21, 31), located opposite the first surface (26f1, 36f1), and having an area greater than that of a cross section of the noble metal tip (28, 38) cut by a plane parallel to the first surface (26f1, 36f1); and a nugget is formed through fusion and solidification resulting from welding at at least a portion of a boundary between the intermediate member (26, 36) and the electrode base metal (21, 31); the spark plug being characterized in that in a section of the spark plug cut by a plane which passes through the center of gravity of the intermediate member (26, 36) and is in parallel with a facing direction between the extending portion and the center electrode, a relational expression S1/(D1 × H1) ≥ 0.005 is satisfied, where S1 is a total area of the nugget, H1 is a height of an end surface of the noble metal tip (28, 38) from a disposition surface (21f, 31bf) of the electrode base metal (21, 31) where the intermediate member (26, 36) is disposed, and D1 is a maximum width of the noble metal tip (28, 38).