A sheet processing device includes a plurality of first units and a second unit. The first units each include, as one unit, a pressing member that presses a folding loop, a frame that movably holds the pressing member in a sheet pressing direction, and an elastic member that is disposed between the frame and the pressing member to bias the pressing member in the sheet pressing direction. The second unit supports, as one unit, a plurality of rows of first units such that the first units of each row are arranged, as a pair, so as to be opposed to each other and that an interval between the pairs is reduced stepwise from a downstream side to an upstream side in a moving direction of the second unit.