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, has a first transport path for guiding the sheet without performing folding processing; a second transport path for performing folding processing on the sheet; a third transport path for guiding the folded sheet towards the carrying-out exit; and a folding processing device disposed in the second transport path to fold the sheet. The second transport path has a path end portion for guiding the sheet to adjust a folding position of the sheet, a nip point to nip the sheet for folding, and a folded sheet guide path for guiding the folded sheet. The first transport path is arranged between the path end portion of the second transport path and the folding processing device.