A paper sorting apparatus includes first to fourth gap measuring units (21A, 21B, 150, 151) to measure gaps between sheets of paper (2). Using the gaps between the sheets (2) varying between the respective gap measuring units, target gap correction values are stored for respective sort shelves (11). In accordance with gaps between sheets (2) changed between the first and second gap measuring units, there are predicted gap variations possibly taking place by when the sheets reach the associated sort shelves (11). Depending on the predicted gap variations, a gap adjuster (10) is controlled to set the gaps to appropriate values at a point where the pertinent sheets reach the associated sort shelves (11).