A sorter has a plurality of sorting tray to receive copied sheets. The sorting trays are moved vertically upon rotation of screw rods. The screw rod has a spiral cam groove with a predetermined cam profile formed on the outer periphery thereof. Cam followers of the sorting tray is engaged with the spiral cam groove. The cam groove is formed such that a distance between adjacent sorting trays in the vertical direction the screw rod is stopped at a first rotational position is different from that when the screw rod is stopped at a second rotational position.