A sheet folding apparatus for performing folding processing, has a first transport path for guiding a sheet from a carry-in entrance to a carrying-out exit without performing the folding processing; a second transport path for performing the folding processing on the sheet from the carry-in entrance; and a folding processing device disposed in a folding position in the second transport path to fold the sheet from the carry-in entrance. The second transport path is disposed to cross the first transport path, and includes a path end portion for guiding the sheet to the folding position, and another path end portion for guiding the folded sheet from the folding position to a downstream side. The path end portion and the another path end portion are disposed opposite to each other relative to the first transport path.