Each time an operation state indicated by operation data measured during normal operation of a refrigerating and air-conditioning apparatus meets an operation data acquisition requirement, the operation data is acquired, and a process of calculating the amount of refrigerant in parts other than an extension pipe and an extension-pipe density on the basis of the acquired data is performed. The internal volume of the extension pipe is calculated on the basis of a group of calculation data items indicating calculations by the process. A standard refrigerant amount is calculated on the basis of the calculated extension-pipe internal volume and the acquired data. The total refrigerant amount in the refrigerant circuit is calculated on the basis of the calculated extension-pipe internal volume and current operation data and is compared to the standard refrigerant amount, thus determining whether the refrigerant is leaked.