To enable entrance of air to a closed space between a brake drum and a back plate through a breather pipe without suction of a foreign matter, such as water and sludge, in a four-wheel vehicle for a work.

Drum brakes 31L and 231R used in rear wheels 3L and 3R of a vehicle form a closed space part to close with a sealant 47R located between brake drums 43L and 43R and back plates 46L and 46R. The ends on one side of breather pipes 32L and 32R are communicated to the closed space formed between the brake drums 43L and 43R of the drum brakes 31L and 31R and the back plates 46L and 46R and the ends on the other side of the breather pipes 32L and 32R are released in an internal space between the side frames 7L and 7R being a hollow member.