Patent ID: 8267391

Claim:
A sheet folding device including: a first folding roller pair that forms a first crease in a sheet; a second folding roller pair that forms a second crease in the sheet; a first stopper member that a leading edge of the sheet transported in a transport direction is pressed against and that places the sheet into position; and a second stopper member that the first crease in the sheet is pressed against and that places the sheet into position, in which the leading edge of the sheet in the transport direction is pressed against the first stopper member such that a position where the first crease in the sheet is to be formed is determined, the position where the first crease is to be formed is guided into a nip portion of the first folding roller pair such that the first crease is formed in the sheet, then the first crease in the sheet is pressed against the second stopper member such that a bend is formed in the sheet and the formed bend is guided into a nip portion of the second folding roller pair such that the second crease is formed in the sheet, the sheet folding device further comprising: a sheet pressing unit that assists the formation of the bend in the sheet and that freely swings to guide the bend into the nip portion of the second folding roller pair, wherein a pivot point of the sheet pressing unit is arranged on a side of the nip portion of the first folding roller pair with respect to a common tangent of the first folding roller pair on a downstream side in the sheet transport direction, and is arranged to be lower than a line that is parallel to a common tangent of the second folding roller pair on an upstream side in the sheet transport direction and that passes through a center of an upper roller of the first folding roller pair.