An air-conditioning system comprising: a heat medium circuit that includes a heat source device whose capacity is variable and a plurality of indoor heat exchangers and that is configured to perform at least one of cooling and heating by circulating a heat medium through the heat source device and the plurality of indoor heat exchangers; a heat-medium conveying device configured to convey the heat medium to the heat medium circuit; a heat-source-device outlet temperature detector configured to detect a temperature of the heat medium flowing out of the heat source device; a plurality of flow control devices configured to control flow rates of streams of the heat medium individually passing through the plurality of indoor heat exchangers; a plurality of inlet heat-medium temperature detectors configured to detect temperatures of the streams of the heat medium individually flowing into the plurality of indoor heat exchangers; a plurality of outlet heat-medium temperature detectors configured to detect temperatures of the streams of the heat medium individually flowing out of the plurality of indoor heat exchangers; a plurality of indoor temperature detectors configured to detect indoor temperatures of rooms in which the plurality of indoor heat exchangers are individually installed; an outdoor air temperature detector configured to detect an outdoor temperature; and a controller configured to control the capacity of the heat source device and the plurality of flow control devices to make the indoor temperatures of the rooms in which the plurality of indoor heat exchangers are individually installed equal to preset temperatures of the rooms, characterized in that the controller is configured to set as a representative indoor heat exchanger an indoor heat exchanger in which the flow rate of the heat medium passing through the indoor heat exchanger has reached an upper limit among the plurality of indoor heat exchangers, detect the indoor temperature of the room in which the representative indoor heat exchanger is installed by using the corresponding indoor temperature detector, determine a target outlet temperature of the heat medium flowing out of the heat source device based on a detection value of the indoor temperature, an inlet heat-medium temperature of the representative indoor heat exchanger, an outlet heat-medium temperature of the representative indoor heat exchanger, the preset temperature of the room in which the representative indoor heat exchanger is installed, and an outdoor air temperature detected by the outdoor air temperature detector, and control the capacity of the heat source device to make the temperature detected by the heat-source-device outlet temperature detector equal to the determined target outlet temperature. a heat medium circuit that includes a heat source device whose capacity is variable and a plurality of indoor heat exchangers and that is configured to perform at least one of cooling and heating by circulating a heat medium through the heat source device and the plurality of indoor heat exchangers; a heat-medium conveying device configured to convey the heat medium to the heat medium circuit; a heat-source-device outlet temperature detector configured to detect a temperature of the heat medium flowing out of the heat source device; a plurality of flow control devices configured to control flow rates of streams of the heat medium individually passing through the plurality of indoor heat exchangers; a plurality of inlet heat-medium temperature detectors configured to detect temperatures of the streams of the heat medium individually flowing into the plurality of indoor heat exchangers; a plurality of outlet heat-medium temperature detectors configured to detect temperatures of the streams of the heat medium individually flowing out of the plurality of indoor heat exchangers; a plurality of indoor temperature detectors configured to detect indoor temperatures of rooms in which the plurality of indoor heat exchangers are individually installed; an outdoor air temperature detector configured to detect an outdoor temperature; and a controller configured to control the capacity of the heat source device and the plurality of flow control devices to make the indoor temperatures of the rooms in which the plurality of indoor heat exchangers are individually installed equal to preset temperatures of the rooms, characterized in that the controller is configured to set as a representative indoor heat exchanger an indoor heat exchanger in which the flow rate of the heat medium passing through the indoor heat exchanger has reached an upper limit among the plurality of indoor heat exchangers, detect the indoor temperature of the room in which the representative indoor heat exchanger is installed by using the corresponding indoor temperature detector, determine a target outlet temperature of the heat medium flowing out of the heat source device based on a detection value of the indoor temperature, an inlet heat-medium temperature of the representative indoor heat exchanger, an outlet heat-medium temperature of the representative indoor heat exchanger, the preset temperature of the room in which the representative indoor heat exchanger is installed, and an outdoor air temperature detected by the outdoor air temperature detector, and control the capacity of the heat source device to make the temperature detected by the heat-source-device outlet temperature detector equal to the determined target outlet temperature.