Creasing device and image forming system

An image forming system comprising:

• a creasing device that forms a crease on a sheet, the creasing device including:
• a first member, extending in a direction perpendicular to a sheet conveying direction, on which a convex blade having a convex cross section is formed;
• a second member, provided at a position to face the first member, on which a groove-like concave blade is formed such that the convex blade can be fitted into the concave blade by interposing the sheet therebetween;
• a drive unit that causes the first member and the second member to be relatively in contact with and separated from each other so as to interpose, therebetween, the sheet that has been stopped at a predetermined position and to form a crease on the sheet;
• a sheet-information acquiring unit that acquires first sheet information of the sheet to be creased;
• a first adjusting unit that adjusts a pressing force exerted by the drive unit;
• and
• a control unit
• that sets the pressing force of the first adjusting unit to an optimum pressing force for the sheet to be creased based on the first sheet information acquired by the sheet-information acquiring unit and
• that causes the drive unit to drive the first member and the second member for creasing the sheet at the optimum pressing force;
• and
• an image forming apparatus that forms an image on the sheet.