Sheet folding apparatus, sheet folding method and image forming apparatus

A sheet folding apparatus, for forming a plurality of folds on the sheet on which an image is formed, comprising:

• a) a first folding section which comprises a first folding roller, a second folding roller in contact with the first roller, and a knife-like first folding plate member for pushing and inserting the first fold of the sheet between the first and second folding rollers;
• and
• b) a second folding section which comprises the second folding roller, a third folding roller in contact with the second folding roller provided downstream from the first folding roller in the sheet feeding direction, a sensor for detecting the passing of the leading edge of the sheet after the first fold being formed, provided upstream from the second folding section and downstream from the first folding section in the sheet feeding direction, and a stopping member for stopping the sheet at a predetermined position by stopping drives of the first and second folding rollers based on the result of detection by the sensor, and a knife-like second folding plate member for pushing and inserting a second fold of the sheet between the second and third folding rollers based on the result of detection by the sensor,
• wherein after the first fold has been formed on the sheet in the first folding section, the second fold of the sheet is formed in the second folding section.