An apparatus for controlling grille aperture ratios of a plurality of air transfer grilles which are installed in a room, includes a determining unit for determining target grille air volumes of air blowing to the racks, for determining simulation air volumes of air blowing from the air transfer grilles on the basis of the target grille air volumes so that each of air of the target grille air volumes are blown to the racks, and for determining grille aperture ratios for each of the air transfer grilles on the basis of the plurality of simulation air volumes so that each of the amounts of air blowing from the air transfer grilles is replaced by each of the simulation air volumes, and a controller for controlling each of the grille aperture ratios of the air transfer grilles on the basis of each of the determined grille aperture ratios.