The present invention provides a sheet folding apparatus comprising a folding means for folding a sheet by feeding a folded portion of the sheet by a pair of rotary members, in which the folded portion of the sheet is passed through a nip between the pair of rotary members by plural times by rotating said pair of rotary members in normal and reverse directions alternately. It further comprises a switch-back control means for controlling so that a return speed of the sheet obtained by the pair of rotary members becomes slower than an advancing speed of the sheet.