A folding system for folding an article that has a main portion and a to-be-folded portion at least on one side of the main portion, the folding system comprising: a carrier section having a carrying surface in contact with the main portion for carrying the main portion; and a folder plate (3A, 3B) provided so as to correspond to the to-be-folded portion, the folder plate (3A, 3B) comprising: a first guide surface provided in parallel to the carrying surface on a side of the carrying surface for guiding the to-be-folded portion of the article before the article is folded; a second guide surface that gradually rises while extending downstream from the first guide surface to raise the to-be-folded portion while being in contact with the to-be-folded portion; and a third guide surface that gradually turns to face the carrying surface while extending downstream from the second guide surface for guiding the to-be-folded portion so that the to-be-folded portion is folded onto the main portion, wherein: the folder plate (3A, 3B) comprises a first folder plate provided on one side of the carrying surface and a second folder plate provided on another side of the carrying surface; and the first and the second folder plates are arranged with a phase difference from each other in a flow direction of the article so that a terminal of the first folder plate is located upstream, in the flow direction, of a terminal of the second folder plate, characterized in that the folding system further comprises a hold plate provided downstream of the terminal of the first folder plate for holding down the article whose to-be-folded portion is folded onto the main portion, and the hold plate includes a slope, the slope being spaced apart above the carrying surface at an upstream end of the hold plate in the flow direction and extending diagonally downward while extending downstream for holding down the article. a carrier section having a carrying surface in contact with the main portion for carrying the main portion; and a folder plate (3A, 3B) provided so as to correspond to the to-be-folded portion, the folder plate (3A, 3B) comprising: a first guide surface provided in parallel to the carrying surface on a side of the carrying surface for guiding the to-be-folded portion of the article before the article is folded; a second guide surface that gradually rises while extending downstream from the first guide surface to raise the to-be-folded portion while being in contact with the to-be-folded portion; and a third guide surface that gradually turns to face the carrying surface while extending downstream from the second guide surface for guiding the to-be-folded portion so that the to-be-folded portion is folded onto the main portion, a first guide surface provided in parallel to the carrying surface on a side of the carrying surface for guiding the to-be-folded portion of the article before the article is folded; a second guide surface that gradually rises while extending downstream from the first guide surface to raise the to-be-folded portion while being in contact with the to-be-folded portion; and a third guide surface that gradually turns to face the carrying surface while extending downstream from the second guide surface for guiding the to-be-folded portion so that the to-be-folded portion is folded onto the main portion, wherein: the folder plate (3A, 3B) comprises a first folder plate provided on one side of the carrying surface and a second folder plate provided on another side of the carrying surface; and the first and the second folder plates are arranged with a phase difference from each other in a flow direction of the article so that a terminal of the first folder plate is located upstream, in the flow direction, of a terminal of the second folder plate, characterized in that the folding system further comprises a hold plate provided downstream of the terminal of the first folder plate for holding down the article whose to-be-folded portion is folded onto the main portion, and the hold plate includes a slope, the slope being spaced apart above the carrying surface at an upstream end of the hold plate in the flow direction and extending diagonally downward while extending downstream for holding down the article.