The present invention is concerning a sheet processing device comprising: a pressing unit that includes a first pressing roller arranged on one side of a thickness direction of a folded sheet bundle, and a second pressing roller and a third pressing roller arranged on the other side across a fold line part of the folded sheet bundle, and a moving unit that moves the pressing unit in a state in which each of a first line and a second line is not parallel to the thickness direction of the folded sheet bundle, the first line connecting the rotational center of the first pressing roller and the rotational center of the second pressing roller, and the second line connecting the rotational center of the first pressing roller and the rotational center of the third pressing roller.