A heating apparatus of a water electrolysis system includes: an enclosure with a draw-in hole; a heating unit accommodated in the enclosure; a blowing unit for directing outside air to the heating unit; a circulation channel for directing part of air heated by the heating unit to a space between the heating unit and the blowing unit; and a draw-out portion for leading the air heated by the heating unit to the outside. The air in the circulation channel is introduced to a space between the heating unit and the blowing unit due to the Venturi effect.