a loading unit configured for loading sheets of glass therein;

a heating unit configured to receive the loading unit having sheets of glass loaded therein, the heating unit includes first to third openings;

a tempering unit connected to the heating unit through the first opening and configured to receive the loading unit having sheets of glass loaded therein, the tempering unit is configured for performing a tempering process on the sheets of glass when the loading unit is positioned in the tempering unit;

a residual salt discharging unit connected to the heating unit through the second opening; and

an auxiliary layer providing unit connected to the heating unit through the third opening of the heating unit, the auxiliary layer providing unit including auxiliary layers for performing a residual salt preprocessing process to increase a removal of residual salt provided on surfaces of the sheets of glass.