Disclosed are compressor-controlling device and method for an air conditioner comprising a plurality of compressors. The compressor-controlling device comprises a movable timer for sensing a stopping time (t) of stopped compressors selected from the plural compressors according to a decrease of a cooling load, a comparison unit for determining whether the stopping time (t) sensed by the movable timer exceeds a designated time (T), and a control unit for re-operating the stopped compressors after a lapse of the designated time (T) when the cooling load is increased, in case the comparison unit judges that the stopping time (t) does not exceed the designated time (T). When the cooling load is increased, the stopped compressors for satisfying the decrease of a cooling load are re-operated after the lapse of the designated time. Therefore, the compressor-controlling device assures the reliability of its system.