Sheet folding mechanism

A sheet folding mechanism, comprising:

• a sheet conveying path that is curved in a sheet conveyance direction;
• a pair of folding rollers that are disposed at a downstream side of the sheet conveying path in the sheet conveyance direction;
• an abutting stopper member that is disposed at the downstream side of the pair of folding rollers in the sheet conveyance direction and that abuts and restricts a leading edge of a conveyed sheet;
• a flexure assist member that assists flexure forming of the sheet abutted to the abutting stopper member;
• a curved conveying guide plate that is located at the sheet conveying path;
• a movable stopper guide plate that is a part of the curved conveying guide plate as being movable along the sheet conveying path by a driving unit;
• and
• a control unit that performs control to vary a movement range of the movable stopper guide plate in accordance with a size of the sheet to be conveyed and a folding mode of the sheet.