An air-conditioning apparatus , comprising: a refrigerant circuit connecting a compressor , a heat source side heat exchanger , an expansion valve , and a use side heat exchanger circularly in order with a refrigerant piping; a compressor heating means heating the compressor when the compressor is not in operation; one of a refrigerant temperature detection means and an outdoor air temperature detection means, the refrigerant temperature detection means detecting a refrigerant temperature (Tr) in the compressor while the compressor is not in operation, the outdoor air temperature detection means detecting at least one of a surrounding temperature and a surface temperature of the heat source side heat exchanger , the temperature detected by the outdoor air detection means being used as the refrigerant temperature (Tr); a temperature sensor detecting a temperature (Ts) of the compressor ; and a controller controlling a heating operation to the compressor , which is carried out by the compressor heating means, characterized in that the controller estimates the amount of a liquid refrigerant (Mr) that has dissolved into a lubricant oil in the compressor (hereinafter, referred to as liquid refrigerant amount) on the basis of the refrigerant temperature (Tr) and the compressor temperature (Ts), using an equation M r =∫F ·(T r - T s) · d t wherein F is a fixed value which is a value obtained by dividing the product of the heat transfer area A and the overall heat transfer coefficient K with the latent heat dH of the refrigerant and assuming that Tr is larger than Ts, and controls the heating operation to the compressor , which is carried out by the compressor heating means, on the basis of the estimated liquid refrigerant amount when the compressor is not in operation. a refrigerant circuit connecting a compressor , a heat source side heat exchanger , an expansion valve , and a use side heat exchanger circularly in order with a refrigerant piping; a compressor heating means heating the compressor when the compressor is not in operation; one of a refrigerant temperature detection means and an outdoor air temperature detection means, the refrigerant temperature detection means detecting a refrigerant temperature (Tr) in the compressor while the compressor is not in operation, the outdoor air temperature detection means detecting at least one of a surrounding temperature and a surface temperature of the heat source side heat exchanger , the temperature detected by the outdoor air detection means being used as the refrigerant temperature (Tr); a temperature sensor detecting a temperature (Ts) of the compressor ; and a controller controlling a heating operation to the compressor , which is carried out by the compressor heating means, characterized in that the controller estimates the amount of a liquid refrigerant (Mr) that has dissolved into a lubricant oil in the compressor (hereinafter, referred to as liquid refrigerant amount) on the basis of the refrigerant temperature (Tr) and the compressor temperature (Ts), using an equation M r =∫F ·(T r - T s) · d t wherein F is a fixed value which is a value obtained by dividing the product of the heat transfer area A and the overall heat transfer coefficient K with the latent heat dH of the refrigerant and assuming that Tr is larger than Ts, and controls the heating operation to the compressor , which is carried out by the compressor heating means, on the basis of the estimated liquid refrigerant amount when the compressor is not in operation. <EOS>