To clear away the operation trouble, relating to an air-conditioning apparatus employing as a substitute refrigerant a mixture refrigerant composed of a low-boiling point refrigerant and a high-boiling point component, that doing cooling with high air temperatures outdoors a rise in the pressure of refrigerant gas containing a low-boiling point refrigerant in a large proportion causes the discharge pressure of the compressor to increase abnormally high.

A vapor-phase refrigerant in a receiver 6 is led into a concentrator 10 and cooled and separated into a gas and liquid; the concentrated vapor of a low-boiling point component is separated and stored in a liquefying tank 11 and the concentrated condensation liquid of a high-boiling point component is returned to the air-conditioning main flow circuit MR. It is also possible that a high-pressure liquid refrigerant sent out from the receiver 6 is separated into a gas and liquid with the interposition of a gas-liquid separator and the concentrator 10, the concentrated vapor of the low-boiling point component is separated and stored in the liquefying tank 11, and the concentrated condensation liquid of the high-boiling point component is returned to the air-conditioning main flow circuit MR.