A sheet folding apparatus includes a first folding unit that folds a sheet of recording medium along first folds that extend orthogonal to a sheet conveying direction, a second folding unit that folds the sheet along a second fold that extends orthogonal to the first fold, a folded-sheet conveying unit that conveys the sheet folded by the first folding unit to the second folding unit, and a stacker unit. The stacker unit is arranged above the folded-sheet conveying unit. The sheet folding apparatus has a first exit through which a non-folded sheet is output, a second exit through which a fan-folded sheet is output, and a third exit through which a cross-folded sheet is output. Sheets output from the first exit and the second exit are stacked in the stacker unit.