Sheet processing apparatus and image forming system

A sheet processing apparatus for performing folding processing in a plurality of portions of a sheet and performing the folding processing so that one end of the sheet exists inside the sheet folded, comprising:

• a transport path including a guide face to guide a transported sheet;
• a transport section adapted to be able to transport the sheet in a first direction for drawing the sheet transported to the transport path, and in a second direction for switching back the drawn sheet in a direction opposite to the direction for drawing;
• a rotating body pair adapted to nip the sheet transported to the transport path by a nip portion to rotate, and thereby perform folding processing on the sheet, including a first circumferential surface with a radius to a rotating body circumferential surface being certain, and a second circumferential surface with a radius smaller than the radius of the first circumferential surface;
• a folding blade adapted to push the sheet transported to the transport path to the nip portion of the rotating body pair;
• and
• a press member adapted to press one end portion of the sheet, which is subjected to the folding processing by the rotating body pair and is transported in the second direction, to guide, including a press portion adapted to press the one end portion of the sheet subjected to the folding processing by the rotating body pair in a direction in which an other end portion of the sheet exists in the transport path in switching back, and a guide portion adapted to guide the sheet pressed by the press portion to the guide face of the transport path where the other end portion of the sheet exists.