A sheet folding device includes a folding unit that applies a fold to a sheet, and a fold-enhancing unit that performs fold enhancement on the sheet applied with the fold by the folding unit. The fold-enhancing unit includes at least two or more rotator pairs each provided with a sheet holding member that holds and pressurizes the sheet applied with the fold so as to enhance the hold. In the at least two or more rotator pairs, the sheet holding member is provided so that an area for holding the sheet shifts from both sides of the sheet toward a central portion of the sheet along a sheet conveying direction from an upstream to a downstream in the fold-enhancing unit.