Sheet folding device

A sheet folding device, comprising:

• a sheet receiving unit comprising a pair of guide plates configured to restrict opposite sides, in a thickness direction, of one or a plurality of stacked sheets introduced into the sheet receiving unit and a striking portion configured to be struck by leading ends of the sheets as introduced;
• a roller group configured to introduce the sheets into the sheet receiving unit, strike the sheets as introduced on the striking portion to form a bent portion on the sheets, and nip and fold the bent portion as formed and discharge the sheets from the sheet receiving unit;
• and
• a curve forming unit configured to form a curved portion on the sheets introduced in the sheet receiving unit, at a position closer to the leading ends of the sheets than a position where the bent portion to be folded by the roller group is formed, the curved portion being curved in a width direction perpendicular to a direction of transfer of the sheets, wherein
• the curve forming unit comprises:
• at least one first protruding member protruding from one of the pair of guide plates toward the other guide plate by a first protruding amount, and having an inclined surface that becomes closer to the other guide plate as the at least one first protruding member extends toward a downstream side in the direction of transfer of the sheets;
• and
• at least one second protruding member protruding from the other guide plate toward the one guide plate by a second protruding amount, and having an inclined surface that becomes closer to the one guide plate as the at least one second protruding member extends toward the downstream side in the direction of transfer of the sheets, wherein
• the at least one first protruding member and the at least one second protruding member are arranged alternately at an interval in the width direction.