To make a bellows section of a boot to be flexibly and repeatedly deformable without deterioration in durability, to thereby reduce rotational resistance when a joint angle is large, the boot has the bellows portion where three or more circumferentially extending crest portions and root portions therebetween are alternately formed. A large-diameter attaching portion is formed at one end of the bellows portion. A small-diameter attaching portion is formed at the other end. A rising wall closest to the large-diameter attaching portion and a rising wall closest to the small-diameter attaching portion have smaller wall thickness than other portions of the bellows section. A ratio (t1/t2) of the thickness (t1) of the rising walls to the thickness (t2) of the other portions of the bellows portion is set to 0.6≦t1/t2