A sheet processing apparatus includes: an output unit that renders one side of a sheet convex and outputs the sheet, the sheet having the one side and other side; a first folding unit that mountain-folds the one side of the sheet, which is rendered to be convex, to form a first fold in the sheet; and a second folding unit that mountain-folds the one side of the sheet, which includes the first fold formed therein, to form a second fold in the sheet.