Sheet folding apparatus and image formation system provided with the apparatus

A sheet folding apparatus for performing folding processing on a sheet in a transporting direction from a carry-in entrance toward a carrying-out exit, comprising:

• a first transport path for guiding the sheet from the carry-in entrance to the carrying-out exit without performing folding processing;
• a second transport path for performing folding processing on the sheet from the carry-in entrance to the carrying-out exit;
• a third transport path connected to the second transport path for guiding the folded sheet towards the carrying-out exit in which a transporting direction of the third transport path is in a direction opposite to a transporting direction in the second transport path;
• and
• a folding processing device disposed in the second transport path to fold the sheet from the carry-in entrance,
• wherein the second transport path has a path end portion above the first transport path for guiding a leading end of the sheet to adjust a folding position of the sheet, a nip point disposed below the first transport path where the sheet is nipped by the folding processing device for folding, and a folded sheet guide path upstream of the nip point for guiding the folded sheet under the first transport path,
• the first transport path is arranged between the path end portion of the second transport path and the folding processing device, and
• the second transport path is arranged between the carry-in entrance to the carrying-out exit in the transporting direction.