A bellows (2) of a dust boot (1, 30) having large diameter parts (3) and small diameter parts (4) disposed alternately covers a piston rod (R) projecting from a cylinder (C). A bump stopper (B) fixed to the cylinder (C) projects into the bellows (2) as a projecting portion. The bellows (2) comprises a first section (M) which passes a projecting end of the projecting portion according to the elongation and contraction of the piston rod (R) and a second section (L) located therebelow. By making the small diameter parts in the second section (L) have a smaller inner diameter than the small diameter part located at a boundary between the first section (M) and the second section (L), the bellows (2) can be made slim without interfering with the bump stopper (B).