A printed unit block aligning device includes a supporting element and an alignment transfer rail. The supporting element is opened and closed between a supporting position and a releasing position. The alignment transfer rail receives the group of the printed unit blocks dropped in response to move of the supporting element to the releasing position, aligns the printed unit blocks in each line unit block in a vertical direction, and feeds the printed unit blocks vertically at a constant speed using alignment transferring element. An electrical controlling element is provided that electrically controls timing of dropping the printed unit blocks from the supporting element onto the alignment transfer rail. While a speed of transfer of the horizontal feeding and transferring element are uniform for any imposition structure, the electrical controlling element controls timing of dropping the printed unit blocks in a manner that depends on the numbers of layers in each vertical line in different imposition structures.