A duplex printing apparatus includes a first conveyance device for supplying recording paper from a first paper supply tray to a printing device; a second conveyance device for supplying the recording paper from a second paper supply tray to the printing device; a third conveyance device for conveying the recording paper printed by the printing device to a paper receiving tray; a fourth conveyance device for conveying the recording paper to the second paper supply tray; a paper switching device disposed at the third conveyance device and operable to selectively send the recording paper printed by the printing device to the second paper receiving tray or to the fourth conveyance device; and a driving mechanism for the second paper supply tray which is operable to move the second paper supply tray to one position for receiving the recording paper from the fourth conveyance device and to another position in which the second paper supply tray supplies the recording paper to the printing device.