A sheet finishing method in which a sheet delivered from an image forming apparatus main body is conveyed and stacked on a sheet placement table, and the stacked sheets are positioned and aligned, and then folded by a folding means composed of a paired folding rollers and a folding plate. The sheet finishing method is controlled such that a rotation motion of the paired folding rollers is switched between a state to be rotated along with an advancing motion of the folding plate and a state to be stopped in accordance with the number of sheets stacked on the sheet placement table.