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.