To solve such a problem that a conventional helmet has an insufficiency in an ability to discharge heat in the helmet.

A protective portion 5a for protecting a ventilation passage 4 is reinforced with reinforcing means for the protective portion. Thereby at least, an area of the cross-section of a heat-guiding portion 10 for guiding the heat in a helmet to the ventilation passage 4 is made nearly the same, and each hole thereof is optionally enlarged, so that the heat can smoothly and efficiently be discharged to the outside of the helmet, and therefore the helmet with a good environment therein (the helmet in which the heat containing a breath expelled by a driver in the helmet rises and is sucked out by a natural reason for drifting natural coolness and reducing stuffiness and fogging of a shield) can be achieved. Furthermore, the JIS regulations can be met, while air passing through the ventilation passage can be adjusted in the helmet and the ability to prevent foreign materials from getting into the ventilation passage can be enhanced.