In order to reduce the possibility that one of a plurality of separators after being slit meanders and is transported while overlapping an adjacent separator: a plurality of separators (12a) are formed by slitting a separator original material (12b) in a transporting direction; and a part of the separators (12a) and another part thereof are separated from a roller (77), which first comes into contact with the separators (12a) having been slit, at different positions on the roller (77) in the circumferential direction thereof.