PURPOSE: To provide comfortableness in any seasons by enabling innumerable air flows without forming a low-pressure zone produced in the rear of a helmet, reducing air resistance by aspirating action, simultaneously promoting aeration of the helmet and ventilating the helmet.

CONSTITUTION: A helmet is composed of two layers and capable of jetting air inhaled from a device 5 from an injection 32 arranged in the center of a Venturi chamber 31, discharging the air from an opening 29 by its synergistic effects and further affecting two sir streams at a varied temperature difference, forming a tornadic state, discharging the air in the helmet by itself, approaching the temperature of the discharged air to the outside air temperature and reducing a low-pressure value (E) without forming turbulent air by the discharged air and reducing the air resistance.