A method in which, while an article is carried with a main portion in contact with a carrying surface and a to-be-folded portion in contact with a folder plate, includes: a first guiding step, wherein a first guide surface guides the to-be-folded portion of the unfolded article, on a side of the carrying surface, in parallel to the carrying surface; a second guiding step, following the first guiding step, wherein a second guide surface, while being in contact with the to-be-folded portion, gradually raises the to-be-folded portion while moving downstream; and a third guiding step, following the second guiding step, wherein a third guide surface guides the to-be-folded portion so that the to-be-folded portion is folded onto the main portion.