A remote controller of an air-conditioning system enables operation state diagnosing. A remote controller of an air-conditioning system having an outdoor device, and an indoor device connected to the outdoor device includes a communication unit that performs bidirectional communication with the indoor device in a wired or wireless manner, and a memory that has stored therein operation-state diagnosing tables for every operation mode that are used in maintenance and inspection of the air-conditioning system. An appropriate one of the operation-state diagnosing tables is used according to an operation mode and an operation time of the air-conditioning system.