A refrigeration cycle comprises a compressor, an indoor heat exchange, an outdoor heat exchanger, a liquid receiver; and a pressure reducer connected in series to form a closed loop. The liquid receiver and the pressure reducer connected in series are connected between the indoor heat exchanger and said outdoor heat exchanger. A non-azeotropic mixture refrigerant comprising at least two kinds of refrigerant of different boiling temperatures mixed together is charged in and circulated through the refrigeration cycle. The mixing ratio of the azeotropic mixture refrigerant circulated thorough the refrigeration cycle is controlled substantially constant.