Provided is a heat pump system that can appropriately manage the number of heat pumps in operation even when any of the heat pumps is defrosting, and that can always operate at a capacity that corresponds to a load. Also provided is an operation method for the heat pump system. A heat pump system (1) wherein a plurality of heat pumps (10A-10C (13A-13D)) are connected to a system load and wherein a system management unit (27) successively calculates the capacity that can be output by the heat pumps (10A-10C (13A-13D)) in operation, compares the calculated capacity value, as a threshold value, to the thermal load of the system load, and manages the number of heat pumps (10A-10C (13A-13D)) in operation.