An air conditioner which includes a compressor, an outdoor heat exchanger, an outdoor expansion valve, and an indoor heat exchanger that have been successively connected by a pipeline, and in which a hydrofluoroolefin-containing refrigerant is to be used, the air conditioner being characterized in that an oxygen adsorption device in which a synthetic zeolite is used as an adsorbent has been disposed somewhere in the pipeline, the synthetic zeolite having a pore diameter which is larger than the size of the oxygen molecule but smaller than the size of the hydrofluoroolefin molecule.