To improve the durability and to enlarge the expandable and contractable range by specifying the number of foldings, a dimension of a folded part and the elongation characteristic of a material with respect to a cross sectional shape of adiaphragm-type bellows.

For example, stainless steel such as SUS 304, SUS 301 and the like, having above 40% of elongation percentage is used as a material of bellows 1. A ratio Rmin/t of a minimum bending radius and a plate thickness in the folded part 2 of the outermost periphery and a fold part 3 of the innermost periphery is at most 0.8. At least three curved parts 4-8 are formed between the folded part 2 of the outermost periphery and the folded part 3 of the innermost periphery. That is, the stress is dispersed to the curved parts 4-8, and not concentrated on both folded parts, so that the impairing of durability can be prevented even when the bellows are used at a tensile side. The concentration of stress is similarly prevented even when the pressure difference is generated between the inside and outside of the bellows 1, so that the durability can be improved.