While the article (1) is conveyed while the main body (10) is in contact with the conveying surface (20) and the folded part (11) is in contact with the folding plates (3A, 3B), the article (1) before folding is processed. Following the first guide step, the first guide surface (31) guides the folded portion (11) on the side of the transport surface (20) in parallel with the transport surface (20), and the second guide. The second guide step in which the surface (32) gradually rises toward the downstream while the surface (32) is in contact with the folded portion (11), and the third guide surface (33 ) Includes a third guide step for guiding the folded portion (11) so that the folded portion (11) is folded over the main body portion (10).本体部(１０)が搬送面(２０)に接し被折り部(１１)が折りプレート(３Ａ，３Ｂ)に接した状態で物品(１)を搬送しながら、折り加工前の物品(１)の被折り部(１１)を搬送面(２０)の側方において搬送面(２０)に平行に第１案内面(３１)が案内する第１案内工程と、第１案内工程に続き、第２案内面(３２)が、被折り部(１１)と接触しつつ被折り部(１１)を下流に向かうに従い徐々に立ち上げる第２案内工程と、第２案内工程に続き、第３案内面(３３)が被折り部(１１)が本体部(１０)に折り重なるように被折り部(１１)を案内する第３案内工程とを備える。
