A paper supply unit including a front cover mounted to a main body of the image forming apparatus to occupy and move between open and closed positions, and, when occupying the opened position, defining a paper receiving space in which printing paper is to be stacked, and a tray cover, disposed to cover the printing paper stacked on the front cover to prevent an inflow of dust or foreign substances, to be inserted into and drawn out of the main body of the image forming apparatus. An image forming apparatus including a main body including a print engine part and a paper supply port, a front cover mounted to a main body of the image forming apparatus to occupy and move between open and closed positions, and, when occupying the opened position, defining a paper receiving space in which printing paper is to be stacked, a tray cover, disposed to cover the printing paper stacked on the front cover to prevent an inflow of dust or foreign substances, to be inserted into and drawn out of the main body of the image forming apparatus and a sliding unit to guide an entrance of the tray cover into the main body and an exit of the tray cover from respect to the main body.