PURPOSE: To properly adjust a moisture content of paper in a paper tray of a copying machine.

CONSTITUTION: A tray of a paper supply device 1 has a tray main unit 10 for storing a paper cassette and a tray cover 20 for covering the tray main unit 10. An electric heater 60 is provided in a bottom part of the tray main unit 10 and connected to a power supply in a copying machine main unit side through a plug 62 and a connector 64. An opening part 24 is provided partly in the tray cover 20 and covered with a dehumidifying cover 80. A solenoid 90 in the copying machine main unit side is energized, when the heater 60 is turned on, to press a lever 86 of the dehumidifying cover 80 by a piston 92, and the cover 80 is opened to discharge moisture in the tray.