A helmet provided with a hat body and an airflow controlling part that is attached to the outer surface of the hat body. The airflow controlling part is provided with two wings arranged on both sides, in the left-right direction, of a portion on the rear side of the outer surface of the hat body. Each of the two wings is connected to a rear lateral portion of the outer surface of the hat body so as to continue from parts of the rear lateral portion and defines a gap. The gap has a curved surface following a part that is of the rear lateral portion and faces the wing. The gap penetrates from the front to the rear between the rear lateral portion and the wing portion and is configured to exhaust the air entering the gap from the front toward the rear lower side.