A spark plug includes a ground electrode that is curved to oppose a tip end surface of a center electrode. A predetermined virtual plane that passes through a center axis of the spark plug along the curved ground electrode faces a flow direction of airflow. The ground electrode includes a main body including: an opposing surface on a first side facing the tip end surface of the center electrode; and a sloped surface on a second side opposite the first side. The main body satisfies 10 [°]≤Dg≤70 [°], 1.0 [mm]≤Th, and 1.5 [mm]≤Wd, where Dg is a slope angle of the sloped surface relative to the opposing surface, Th is a thickness of the main body in an insertion direction of the center electrode, and Wd is a width of the ground electrode in a direction perpendicular to the virtual plane.