SHEET FOLDING DEVICE, SHEET PROCESSING DEVICE, IMAGE FORMATION SYSTEM AND SHEET FOLDING METHOD

To provide a technique which allows easy entrance of a sheet bundle having the high folding height.SOLUTION: A sheet folding device which sequentially forms a fold on a sheet by alternately using a pair of folding rollers for respectively forming folds on a sheet includes: additional-folding means which has a rotary member that is provided with a protrusion part extending in the rotational shaft direction on the outer peripheral surface and performs additional-folding processing of pressing the fold formed with the pair of folding rollers with the protrusion part; and a control unit which changes the position of the protrusion part in accordance with the height of the tip part of the sheet conveyed to the additional-folding means and causes the additional-folding means to perform the additional-folding processing after bringing the protrusion part into contact with the tip part upper surface of the sheet conveyed by rotating the rotary member.SELECTED DRAWING: Figure 7 【課題】折り高さの高いシート束を容易に進入させることができる技術を提供する。【解決手段】シートに折り目をそれぞれ形成する一対の折りローラを交互に用いてシートに折り目を順次形成するシート折り装置であって、回転軸方向に延在する突起部が外周面上に設けられている回転部材を有し、一対の折りローラで形成された折り目を突起部で押圧する増し折り処理を行う増し折り手段と、増し折り手段に搬送されるシートの先端部の高さに応じて、突起部の位置を変更し、回転部材を回転させることで搬送されてくるシートの先端部上面に突起部を当接させた後に、増し折り手段に増し折り処理を行わせる制御部と、を備える。【選択図】図７