To provide a bolt capable of surely fastening even a thin member, and performing a tight fastening with an opponent member, similar to such as a wet preventing bolt and a masking bolt for female screw protection.

An incomplete thread 5A of an end 51A of an under head screw part 5 of a head 2 of the bolt 1 is made to be minimum, and a knotting part 14A is formed contiguous to the end 51A. Accordingly, a nut 8 threadedly engaged to the under head of the bolt 1 is guided to immediately before or to be in close contact with the under head of the head 2 of the bolt 1.