Sheet folding apparatus and image forming system

A sheet folding apparatus, comprising:

• a conveying roller pair that conveys a sheet;
• a first folding roller pair that folds the sheet conveyed from the conveying roller pair;
• a second folding roller pair that folds the sheet conveyed from the conveying roller pair in conjunction with the first folding roller pair, the second folding roller pair being arranged opposite to the first folding roller pair such that there is a predetermined gap therebetween;
• and
• a control circuit configured to control conveying the sheet with the conveying roller pair and to control folding the sheet with the first folding roller pair and the second folding roller pair,
• wherein the control circuit controls the apparatus so that a sheet conveying speed or a sheet conveying amount of the conveying roller pair is different from a sheet conveying speed or a sheet conveying amount of the first folding roller pair or the second folding roller pair when a folded part of a folded sheet is guided between the first folding roller pair and the second folding roller pair;
• the control circuit controls the apparatus such that a sheet conveying force of the conveying roller pair is different from a sheet conveying force of the first folding roller pair or the second folding roller pair;
• and
• the control circuit controls when the sheet is conveyed from the first folding roller pair or the second folding roller pair to the conveying roller pair.