A sheet processing apparatus includes a folding roller unit configured to form a fold in a sheet while the sheet passes through a nip of rollers, and a fold-enhancing roller unit having a first roller, a second roller, and a third roller, the first roller being provided facing a first surface of the sheet, orthogonal to a direction of transport of the sheet, the second and third rollers being provided facing a second surface of the sheet orthogonal to the direction of transport of the sheet and different from the first surface, the second and third rollers forming nips with the first roller, in which the fold-enhancing roller unit is moved along the fold with the sheet nipped in the nip between the first roller and the second roller and in the nip between the first roller and the third roller, to form a fold.