The sheet pressing apparatus includes an inlet port configured to receive a sheet having a folding line; additional-folding rollers arranged downstream of the inlet port and configured to press the sheet at the folding line; a lower folding guide opposing the additional-folding rollers; a first drive mechanism configured to move the additional-folding rollers between a pressing position, at which the additional-folding rollers approach the lower folding guide to press the sheet at the folding line, and a retreat position to which the additional-folding rollers are moved with respect to the lower folding guide from the pressing position; a second drive mechanism configured to move the additional-folding rollers along the folding line; and a restriction member configured to restrict, at a preset restriction position, the sheet thickness at the folding line to a value equal to or less than a prescribe value, while the additional-folding rollers are moving.