A controller controls the operations of a humidity control apparatus and an air conditioner. The controller includes a power consumption detector, a target value setting processor, and an operation control unit. The power consumption detector detects the power consumption of the humidity control apparatus and the air conditioner. The target value setting processor performs optimal target value setting processing by performing first or second processing. The first processing lowers a target operating frequency of a humidity controlling compressor and a target evaporation temperature in a utilization-side heat exchanger. The second processing raises the target operating frequency and the target evaporation temperature. The optimal target value setting processing sets the target operating frequency and the target evaporation temperature so as to minimize the power consumption. The operation control unit controls the humidity control apparatus to achieve the target operating frequency and the air conditioner to achieve the target evaporation temperature.