A controller controls the number of the heat source units to be operated and an amount of the heat-transfer medium which flows to the load side in accordance with required capability from the load side. The controller detects the flow rate of the heat-transfer medium flowing to the load side, and controls an amount of the heat-transfer medium which bypass flowing to the load side in accordance with the detected flow rate. The controller divides the detected flow rate and allocates the divided flow rate to each of the heat source units in operation, thereby controlling a power of the pump in each of the heat source units in operation in accordance with the allocated amount.