Abstract: A sheet sorting apparatus which easily sorts sheets into groups, and makes these groups readily distinguishable on a single output tray. According to an aspect of the invention, there is provided a sheet sorting apparatus located at the sheet outlet location of an image processing device, the sheet sorting apparatus including a marker attaching mechanism for attaching markers at a certain position on the output sheets. The marker attaching mechanism includes a tape feeding device in which the tape has an adhesive surface along one side edge, a cutter for making a marker by cutting the tape at a preset length, guides for positioning the marker in the proper location on the output sheet, a marker attaching roller, and a feeder for feeding the sheet and marker together. The feeder presses the marker against the sheet to attach it. The advantages of the invention include the markers for separating the groups being attached to the sheets, so they will not fall out if the sheets are removed from the output tray.