Provided is a sheet folding apparatus for folding a sheet stack, including a sheet stack support member for supporting a sheet stack by being abutted against a lower edge of the sheet stack, an abutting member for folding the sheet stack by making the sheet stack supported by the sheet stack support member abutted against a leading edge of the abutting member, and paired folding rollers for sandwiching the sheet stack folded by the abutting member to fold the sheet stack at a fold position, in which a position where the sheet stack is abutted against the leading edge of the abutting member with respect to the fold position is varied based on sheet stack information.