Sheet pressing means (59) is provided that assists the formation of a bend in a sheet (S) and that freely swings to guide the bend into the nip portion of a second folding roller pair (a second roller (54) and a third roller (55)). The pivot point (594) of the sheet pressing mean (59) is arranged on the side of the nip portion of a first folding roller pair with respect to a common tangent (L1) of the first folding roller pair (a first roller (53) and the second roller (54)) on the downstream side in a sheet transport direction, and is arranged to be lower than a line (L3) that is parallel to a common tangent (L2) of the second folding roller pair on the upstream side in the sheet transport direction and that passes through the center (O) of the first roller (53). Thus, it is possible to reliably perform processing for folding the sheet in a predetermined position regardless of the material quality, the thickness and the like of the sheet. Even if a strong force is applied to the sheet pressing means at the time of processing for handing a paper jam or the like, the sheet pressing means is unlikely to be deformed, and it is possible to stably perform the folding processing for a long period of time.