PURPOSE: To make mounting or demounting ever so easy as well as to improve the extent of setting and engaging accuracies, by forming a notch at the discharge side of printing paper for an image printer, while engaging one side of setting members for a paper sorter with this notch, and having the other side engaged with an engaging device of the paper sorter.

CONSTITUTION: The setting device is provided with an image printer and a paper sorter 3, while the setting member 4 fitted with a projecting piece 4a and another projecting piece 4b projected horizontally is designed so as to be engaged when the projecting piece 4a is inserted into the notch 5a formed in substrate 5 at the side of a printing paper discharge part of the image printer. The paper sorter 3 is provided with a bolt 6 and a slide plate 7 is designed so as to be engaged with the projecting piece 4b of the setting member 4 by means of thread fitting and hold it. Therefore, when the paper sorter 3 is attached to the image printer, the projecting piece 4a of the setting member 4 is put back to horizontality while inserting it into the notch 5a with the paper sorter tilted, and it is mounted on a botton plate 8. At this time, the slide plate 7 is slidden up and down and the setting member 4 is positioned right.