A heat pump chilling system in which a plurality of heat pump chilling devices (2A to 2E) provided with refrigeration cycles through which refrigerant flows are connected in parallel with a load and in which a heat medium having exchanged heat with the refrigerant in the plurality of heat pump chilling devices (2A to 2E) circulates to the load, wherein the plurality of heat pump chilling devices (2A to 2E) are configured to have the same operating capacities, the heat pump chilling system comprising: an inlet temperature sensor detecting a temperature of the heat medium flowing into the plurality of heat pump chilling devices (2A to 2E) from the load as an inlet temperature (Ti); an outlet temperature sensor detecting a temperature of the heat medium flowing into the load from the plurality of heat pump chilling devices (2A to 2E) as an outlet temperature (To); and a system control device configured to control operation of the plurality of heat pump chilling devices (2A to 2E) based on the inlet temperature (Ti) detected in the inlet temperature sensor and the outlet temperature (To) detected in the outlet temperature sensor, characterized by the system control device including a storage unit configured to store an operating capacity (Td) for each of the plurality of heat pump chilling devices (2A to 2E), a requested-capacity calculating unit configured to calculate a requested capacity (Tdg) based on the inlet temperature (Ti) or the outlet temperature (To) and a set target temperature (Tref), a number-of-devices calculating unit configured to calculate the number of devices to be activated among the plurality of heat pump chilling devices (2A to 2E) satisfying the requested capacity (Tdg) calculated by the requested-capacity calculating unit based on the operating capacity (Td) stored in the storage unit for each of the plurality of heat pump chilling devices (2A to 2E), an activation control unit configured to activate the plurality of heat pump chilling devices of the number of devices to be activated calculated in the number-of-devices calculating unit by activating a single one of the plurality of heat pump chilling devices alone at a start of operation and then simultaneously activating zero or more of the plurality of heat pump chilling devices of the remaining number of the number of devices to be activated calculated in the number-of-devices calculating unit, and an operating-capacity calculating unit configured to calculate the operating capacity (Td) of the single activated heat pump chilling device based on the inlet temperature (Ti) and the outlet temperature (To) after the single heat pump chilling device is activated, and store the calculated operating capacity (Td) into the storage unit as the operating capacity (Td) of each of the plurality of heat pump chilling devices (2A to 2E). an inlet temperature sensor detecting a temperature of the heat medium flowing into the plurality of heat pump chilling devices (2A to 2E) from the load as an inlet temperature (Ti); an outlet temperature sensor detecting a temperature of the heat medium flowing into the load from the plurality of heat pump chilling devices (2A to 2E) as an outlet temperature (To); and a system control device configured to control operation of the plurality of heat pump chilling devices (2A to 2E) based on the inlet temperature (Ti) detected in the inlet temperature sensor and the outlet temperature (To) detected in the outlet temperature sensor, characterized by the system control device including a storage unit configured to store an operating capacity (Td) for each of the plurality of heat pump chilling devices (2A to 2E), a requested-capacity calculating unit configured to calculate a requested capacity (Tdg) based on the inlet temperature (Ti) or the outlet temperature (To) and a set target temperature (Tref), a number-of-devices calculating unit configured to calculate the number of devices to be activated among the plurality of heat pump chilling devices (2A to 2E) satisfying the requested capacity (Tdg) calculated by the requested-capacity calculating unit based on the operating capacity (Td) stored in the storage unit for each of the plurality of heat pump chilling devices (2A to 2E), an activation control unit configured to activate the plurality of heat pump chilling devices of the number of devices to be activated calculated in the number-of-devices calculating unit by activating a single one of the plurality of heat pump chilling devices alone at a start of operation and then simultaneously activating zero or more of the plurality of heat pump chilling devices of the remaining number of the number of devices to be activated calculated in the number-of-devices calculating unit, and an operating-capacity calculating unit configured to calculate the operating capacity (Td) of the single activated heat pump chilling device based on the inlet temperature (Ti) and the outlet temperature (To) after the single heat pump chilling device is activated, and store the calculated operating capacity (Td) into the storage unit as the operating capacity (Td) of each of the plurality of heat pump chilling devices (2A to 2E).