To provide new bellows, which are made even by an inexperienced person easily, reduce a cost for manufacture, and effectively prevent each core material from shifting, and a method of manufacturing the bellows.

The bellows 1 are equipped with a flexible tubular sheet body 2 formed into a tubular shape and a plurality of tubular core materials 3 which are placed in the tubular sheet body 2 and have the outer peripheral surfaces each making contact with at least a part of the inner peripheral surface of the tubular sheet body 2 with pressure. The bellows 1 have mountain-fold parts 1a where each of the core materials 3 is placed and valley-fold parts 1b between the mountain-fold parts 1a, 1a to expand and contract the bellows 1. Thin parts 2a made thinner than the other parts are formed on the tubular sheet body 2, and the outer peripheral surfaces of the core materials 3 make contact with the positions where the thin parts 2a are formed with pressure.