A boot is made of a resin for covering a ball joint interposed between a larger diameter mating member and a small diameter mating member, including a large diameter attachment portion fixed to the large diameter mating member, a first bellows portion continuous to the large diameter attachment portion, a second bellows portion which is continuous to the first bellows portion and in which at least a bottom inner peripheral diameter thereof is not larger than that of the first bellows portion and a rigidity in a radial direction thereof is lower than that of the first bellows portion, a taper bellows portion continuous to the second bellows portion, and a small diameter attachment portion continuous to the taper bellows portion and fixed to the small diameter mating member.