To determine a leakage of a refrigerant even when an inexpensive, rotating-speed-controllable compressor is employed.

An air conditioner includes a compressor 9, an outdoor unit 1 having an outdoor heat exchanger 11 and an outdoor expansion valve 12, and an indoor unit 2 having an indoor heat exchanger 6, and connects the outdoor unit and an indoor unit by refrigerant pipes to constitute a refrigeration cycle. Further, the air conditioner includes: an ambient temperature detector 13; a discharge side temperature detector 14 for the compressor; a controller 15 which controls the compressor and outdoor expansion valve; a storage device 17 which stores an ambient temperature at the start of the compressor in an initial stage after installation of the compressor, and a discharge-side temperature of the compressor when the air conditioner operates under a prescribed condition; and an arithmetic unit 16 which determines a leakage of a refrigerant by comparing an ambient temperature at the start of the compressor and a discharge-side temperature of the compressor when the air conditioner thereafter operates under the prescribed condition with the ambient temperature in the initial stage and the discharge-side temperature of the compressor which are stored in the storage device.