A spark plug comprising: a center electrode (20, 21) including a center electrode body (21, 21) extending in an axial direction and a center electrode tip joined to a front end (E1, E2) of the center electrode body (21 A, 21); an insulator (10, 12) having an axial hole (12, 13) extending in the axial direction, wherein the center electrode (20, 21) is arranged in the axial hole (12, 13); a metal shell (50, 51) arranged around an outer circumference of the insulator (10,12); and a ground electrode (30, 31) including a ground electrode body (31X, 31, 33) electrically connected to the metal shell (50, 51) and a projection part that is a portion projecting toward the center electrode (20, 21) from an end (E1, E2, E3, E4) part of the ground electrode body (31 X, 31, 33) and includes a ground electrode tip (39X, 39, 40) forming a gap between itself and the center electrode tip, wherein, in a particular cross section including a center axis of the center electrode tip, when two directions that are orthogonal to a center axis of the center electrode tip and opposed to each other are denoted as a first direction and a second direction, an outer diameter (R1, R2) of a first face that is a face of the center electrode tip forming the gap is denoted as R1, an outer diameter (R1, R2) of a second face that is a face of the ground electrode tip (39X, 39, 40) forming the gap is denoted as R2, a length (L1, L2, W1, W2) of the gap is denoted as G1, and an average distance of a distance between an end (E1, E2, E3, E4) in the first direction of the first face and an end (E1, E2, E3, E4) in the first direction of the second face and a distance between an end (E1, E2, E3, E4) in the second direction of the first face and an end (E1, E2, E3, E4) in the second direction of the second face is denoted as G2, R1 < R2, 0.5 mm ≤R1 ≤ 1.1 mm, 0.7 mm ≤ R2 ≤ 1.2 mm, 0.6 mm ≤ G1 ≤ 1.3 mm, and 1.4 ≤ (R2/R1) × (G2/G1) ≤ 1.8 are satisfied; wherein the ground electrode body (31X, 31, 33) is a bar-shaped member including a base material that is a portion forming at least a part of a surface of the ground electrode body (31X, 31, 33) and a core part buried in the base material and having a higher thermal conductivity than the base material, and wherein, when a length (L1, L2, W1, W2) in a longitudinal direction of a portion including the core part of the ground electrode body (31X, 31, 33) along a shape of the ground electrode body (31X, 31, 33) is denoted as L and a length (L1, L2, W1, W2) in the axial direction from a front end (E1, E2, E3, E4) of the metal shell (50, 51) to a front end (E1, E2, E3, E4) of the ground electrode (30, 31) is denoted as C, 0.98 ≤ (L/C) ≤ 1.48 is satisfied. a center electrode (20, 21) including a center electrode body (21, 21) extending in an axial direction and a center electrode tip joined to a front end (E1, E2) of the center electrode body (21 A, 21); an insulator (10, 12) having an axial hole (12, 13) extending in the axial direction, wherein the center electrode (20, 21) is arranged in the axial hole (12, 13); a metal shell (50, 51) arranged around an outer circumference of the insulator (10,12); and a ground electrode (30, 31) including a ground electrode body (31X, 31, 33) electrically connected to the metal shell (50, 51) and a projection part that is a portion projecting toward the center electrode (20, 21) from an end (E1, E2, E3, E4) part of the ground electrode body (31 X, 31, 33) and includes a ground electrode tip (39X, 39, 40) forming a gap between itself and the center electrode tip,