PURPOSE: To double the number of bins as well as to use a transport part and an indexer part in common to reduce a manufacturing cost, and to save an installation space, by a method wherein a basic sorter unit is coupled to an additional bin unit.

CONSTITUTION: A basic sorter unit 1 is provided with a horizontal transport 2, a paper path switching device 3, a vertical transport 4, a two-way indexer 5, and bins 6. Meanwhile, only a number of the bins 6 are disposed in an additional bin unit 16, and after the right cover of the basic sorter unit 1 is removed, both units 1 and 16 are coupled to each other in one body to form a paper sorter. In this case, when the paper path switching device 3 is laid down rightward, the paper sheets ae sorted in the bins 6 on the basic sorter unit 1 side, and when laid down leftward, the paper sheets are sorted in the bins 6 on the additional bin unit 16 side.