PURPOSE: To obtain a protective cap having a good aeration and ventilation.

CONSTITUTION: Outside air is flowed to the inside and outside of a cap portion 10 by making the inside of an inner layer 10A of the cap portion 10 communicate with the outside of an outer layer 10B through ventilation holes 20A, a gap 12 and ventilation holes 20B. However, since the ventilation holes 20A and 20B of both layers 10A and 10B are constructed not to overlap each other, a falling substance or flying material can not penetrate into the inside of the cap portion 10. Spacers 14 arranged at proper positions within the gap 12, are fulfilling a role of fixing the previously mentioned inner layer 10A and outer layer 10B as one piece and at the same time holding the gap 12 properly to secure an air flow route.