A heat pump apparatus comprising: a compressor; a condenser; an expansion mechanism; and an evaporator, the compressor, the condenser, the expansion mechanism, and the evaporator being configured to perform a refrigeration cycle, the heat pump apparatus being configured to perform heat transfer in the condenser or the evaporator, the compressor including a sealed container, a compression mechanism mounted inside the sealed container, and an electric motor configured to rotatively drive the compression mechanism, the compression mechanism being configured to compress a refrigerant, and to be lubricated by a refrigerating machine oil, the electric motor including a stator fixed to the sealed container, with a winding wire being wound around the stator through intermediation of an insulating material, and a rotor surrounded by the stator, wherein the insulating material comprises a wholly aromatic liquid crystal polyester having a molecular main chain constituted by a monomer including p-hydroxybenzoic acid as an essential monomer and a monomer solely including benzene-ring as another monomer via an ester bond, characterised in that the refrigerating machine oil has a saturated water content of 2% or less at 40 degrees C and a relative humidity of 80%, for 24 Hr, wherein the refrigerant comprises a multi-component substance containing difluoromethane (HFC-32) and ethylene-based fluorohydrocarbon, and the ratio of the ethylene-based fluorohydrocarbon to the difluoromethane (HFC-32) is 70 wt% or less. a compressor; a condenser; an expansion mechanism; and an evaporator, the compressor, the condenser, the expansion mechanism, and the evaporator being configured to perform a refrigeration cycle, the heat pump apparatus being configured to perform heat transfer in the condenser or the evaporator, the compressor including a sealed container, a compression mechanism mounted inside the sealed container, and an electric motor configured to rotatively drive the compression mechanism, the compression mechanism being configured to compress a refrigerant, and to be lubricated by a refrigerating machine oil, a sealed container, a compression mechanism mounted inside the sealed container, and an electric motor configured to rotatively drive the compression mechanism, the compression mechanism being configured to compress a refrigerant, and to be lubricated by a refrigerating machine oil, the electric motor including a stator fixed to the sealed container, with a winding wire being wound around the stator through intermediation of an insulating material, and a rotor surrounded by the stator, a stator fixed to the sealed container, with a winding wire being wound around the stator through intermediation of an insulating material, and a rotor surrounded by the stator, wherein the insulating material comprises a wholly aromatic liquid crystal polyester having a molecular main chain constituted by a monomer including p-hydroxybenzoic acid as an essential monomer and a monomer solely including benzene-ring as another monomer via an ester bond, characterised in that the refrigerating machine oil has a saturated water content of 2% or less at 40 degrees C and a relative humidity of 80%, for 24 Hr, wherein the refrigerant comprises a multi-component substance containing difluoromethane (HFC-32) and ethylene-based fluorohydrocarbon, and the ratio of the ethylene-based fluorohydrocarbon to the difluoromethane (HFC-32) is 70 wt% or less.