In an air conditioner, during an operation, a gas-liquid two-phase non-azeotropic mixture refrigerant enters a receiver and accumulates in the receiver in a state where a gas phase and a liquid phase are separated. For example, when the non-azeotropic mixture refrigerant includes two components, i.e., a high-boiling refrigerant and a low-boiling refrigerant, the controller may estimate the ratio (composition ratio) between the low-boiling refrigerant and the high-boiling refrigerant in each of the gas phase and the liquid phase based on the temperature and the pressure of the non-azeotropic mixture refrigerant in the receiver. Thus, the controller may estimate the composition ratio of the liquid-phase non-azeotropic mixture refrigerant flowing out of the receiver as the composition ratio of the non-azeotropic mixture refrigerant circulating in the refrigerant circuit.