An air-conditioning system comprising: a heat source apparatus; a plurality of indoor units (30a, 30b, 30c); a relay device; a refrigerant circuit; and a heat medium circuit, the heat source apparatus including a compressor, a flow switching valve, and a heat-source-side heat exchanger, the plurality of indoor units (30a, 30b, 30c) each including an indoor-side heat exchanger, the relay device including a pump and an inter-medium heat exchanger; the refrigerant circuit being provided as a circuit in which the compressor, the flow switching valve, the heat-source-side heat exchanger, and the inter-medium heat exchanger are connected by refrigerant pipes and refrigerant is circulated, the heat medium circuit being provided as a circuit in which the pump, the inter-medium heat exchanger, and the indoor-side heat exchanger of each of the plurality of indoor units (30a, 30b, 30c) are connected by heat medium pipes and a heat medium is circulated, the air-conditioning system further comprising: flow-rate detection devices each provided in an associated one of the plurality of indoor units (30a, 30b, 30c), and each configured to detect flow-rate information regarding a flow rate of the heat medium in the associated indoor unit (30a, 30b, 30c); and a controller configured to control, when the flow-rate information detected by the flow-rate detection devices is abnormal flow-rate information indicating presence of a control target indoor unit (30a, 30b, 30c) which is an indoor unit (30a, 30b, 30c) to be controlled of the plurality of indoor units (30a, 30b, 30c) and in which a flow of the heat medium is cut off, an operation of at least one of the compressor, the pump, and the control target indoor unit (30a, 30b, 30c), wherein each of the plurality of indoor units (30a, 30b, 30c) includes an indoor-side fan and a flow control valve configured to adjust the flow rate of the heat medium, the controller is configured to close the flow control valve of the control target indoor unit (30a, 30b, 30c) after stopping the indoor-side fan of the control target indoor unit (30a, 30b, 30c), and the controller is configured to calculate a required flow rate of the heat medium in the indoor units (30a, 30b, 30c) excluding the control target indoor unit (30a, 30b, 30c), and reduce, when the required flow rate is lower than a threshold for a flow rate of the heat medium that is determined in advance, a rotation speed of the pump until the required flow rate reaches the threshold. flow-rate detection devices each provided in an associated one of the plurality of indoor units (30a, 30b, 30c), and each configured to detect flow-rate information regarding a flow rate of the heat medium in the associated indoor unit (30a, 30b, 30c); and a controller configured to control, when the flow-rate information detected by the flow-rate detection devices is abnormal flow-rate information indicating presence of a control target indoor unit (30a, 30b, 30c) which is an indoor unit (30a, 30b, 30c) to be controlled of the plurality of indoor units (30a, 30b, 30c) and in which a flow of the heat medium is cut off, an operation of at least one of the compressor, the pump, and the control target indoor unit (30a, 30b, 30c), wherein each of the plurality of indoor units (30a, 30b, 30c) includes an indoor-side fan and a flow control valve configured to adjust the flow rate of the heat medium, the controller is configured to close the flow control valve of the control target indoor unit (30a, 30b, 30c) after stopping the indoor-side fan of the control target indoor unit (30a, 30b, 30c), and the controller is configured to calculate a required flow rate of the heat medium in the indoor units (30a, 30b, 30c) excluding the control target indoor unit (30a, 30b, 30c), and reduce, when the required flow rate is lower than a threshold for a flow rate of the heat medium that is determined in advance, a rotation speed of the pump until the required flow rate reaches the threshold.