An image forming system comprising: An image forming apparatus that forms an image on a sheet; and a sheet processing apparatus that forms a folding line on the conveyed sheet on which the image is formed by the image forming apparatus, the sheet processing apparatus comprising: a bend forming unit including a first bend forming roller and a second bend forming roller that rotate around rotation axes that are in a direction that is perpendicular to a conveying direction of the sheet and that is parallel to a surface of the sheet to nip and hold both surfaces of the conveyed sheet and form a bend on the sheet; a conveying unit that conveys the sheet toward the bend forming unit such that, when a vector in a conveying direction of the sheet that is conveyed to the bend forming unit is decomposed into vectors in a direction of a tangent line at a contact point between a conveyance path of the sheet and a surface of the first bend forming roller and in a direction perpendicular to the tangent line, the vector in the direction of the tangent line includes a component in a direction from the contact point toward the second bend forming roller; and a folding line forming unit (350, 370) that is located on an opposite side of the second bend forming roller with respect to the contact point and that presses the bend formed on the conveyed sheet from the surface of the sheet so as to form a folding line on the sheet, characterised in that the bend forming unit nips both surfaces of the sheet that is conveyed by the conveying unit while rotating the first bend forming roller and the second bend forming roller on a downstream side of the conveying unit in the conveying direction so as to convey the sheet for a predetermined distance while maintaining a position of the formed bend on the sheet and, after conveying the sheet for the predetermined distance, reverses rotation directions of the first bend forming roller and the second bend forming roller to move the formed bend toward the folding line forming unit (350, 370). An image forming apparatus that forms an image on a sheet; and a sheet processing apparatus that forms a folding line on the conveyed sheet on which the image is formed by the image forming apparatus, the sheet processing apparatus comprising: a bend forming unit including a first bend forming roller and a second bend forming roller that rotate around rotation axes that are in a direction that is perpendicular to a conveying direction of the sheet and that is parallel to a surface of the sheet to nip and hold both surfaces of the conveyed sheet and form a bend on the sheet; a conveying unit that conveys the sheet toward the bend forming unit such that, when a vector in a conveying direction of the sheet that is conveyed to the bend forming unit is decomposed into vectors in a direction of a tangent line at a contact point between a conveyance path of the sheet and a surface of the first bend forming roller and in a direction perpendicular to the tangent line, the vector in the direction of the tangent line includes a component in a direction from the contact point toward the second bend forming roller; and a folding line forming unit (350, 370) that is located on an opposite side of the second bend forming roller with respect to the contact point and that presses the bend formed on the conveyed sheet from the surface of the sheet so as to form a folding line on the sheet, a bend forming unit including a first bend forming roller and a second bend forming roller that rotate around rotation axes that are in a direction that is perpendicular to a conveying direction of the sheet and that is parallel to a surface of the sheet to nip and hold both surfaces of the conveyed sheet and form a bend on the sheet; a conveying unit that conveys the sheet toward the bend forming unit such that, when a vector in a conveying direction of the sheet that is conveyed to the bend forming unit is decomposed into vectors in a direction of a tangent line at a contact point between a conveyance path of the sheet and a surface of the first bend forming roller and in a direction perpendicular to the tangent line, the vector in the direction of the tangent line includes a component in a direction from the contact point toward the second bend forming roller; and a folding line forming unit (350, 370) that is located on an opposite side of the second bend forming roller with respect to the contact point and that presses the bend formed on the conveyed sheet from the surface of the sheet so as to form a folding line on the sheet, characterised in that the bend forming unit nips both surfaces of the sheet that is conveyed by the conveying unit while rotating the first bend forming roller and the second bend forming roller on a downstream side of the conveying unit in the conveying direction so as to convey the sheet for a predetermined distance while maintaining a position of the formed bend on the sheet and, after conveying the sheet for the predetermined distance, reverses rotation directions of the first bend forming roller and the second bend forming roller to move the formed bend toward the folding line forming unit (350, 370).