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, wherein the compressor includes a sealed container, a compression mechanism mounted inside the sealed container, and an electric motor configured to rotate and drive the compression mechanism, the compression mechanism being configured to compress refrigerant, and to be lubricated by a refrigerating machine oil, wherein the electric motor includes a stator fixed to the sealed container with a winding being wound around the stator through intermediation of an insulating material, and a rotator surrounded by the stator, wherein the insulating material includes wholly aromatic liquid crystal polyester having a main chain of a molecule through an ester bond, the wholly aromatic liquid crystal polyester containing p-hydroxybenzoic acid as a monomer of essential component, and a monomer having a benzene ring, as an other monomer, only the monomer of essential component and the other monomer are forming the ester bond, wherein the wholly aromatic liquid crystal polymer is obtained by polycondensation of a total of five or six kinds of monomers as monomers forming the ester bond among from the monomers containing, as the monomer of essential component, p-hydroxybenzoic acid, and the monomers containing, as a monomer of additive component, 4,4'-biphenol, hydroquinone, terephthalic acid, isophthalic acid, and/or 6-hydroxy-2-naphthoic acid, and wherein a saturated water amount of the refrigerating machine oil is 0.5% or more and 1% or less at 40 degrees Celsius and a relative humidity of 80%. 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, 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, wherein the compressor includes a sealed container, a compression mechanism mounted inside the sealed container, and an electric motor configured to rotate and drive the compression mechanism, the compression mechanism being configured to compress 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 rotate and drive the compression mechanism, the compression mechanism being configured to compress refrigerant, and to be lubricated by a refrigerating machine oil, wherein the electric motor includes a stator fixed to the sealed container with a winding being wound around the stator through intermediation of an insulating material, and a rotator surrounded by the stator, a stator fixed to the sealed container with a winding being wound around the stator through intermediation of an insulating material, and a rotator surrounded by the stator, wherein the insulating material includes wholly aromatic liquid crystal polyester having a main chain of a molecule through an ester bond, the wholly aromatic liquid crystal polyester containing p-hydroxybenzoic acid as a monomer of essential component, and a monomer having a benzene ring, as an other monomer, p-hydroxybenzoic acid as a monomer of essential component, and a monomer having a benzene ring, as an other monomer, only the monomer of essential component and the other monomer are forming the ester bond, wherein the wholly aromatic liquid crystal polymer is obtained by polycondensation of a total of five or six kinds of monomers as monomers forming the ester bond among from the monomers containing, as the monomer of essential component, p-hydroxybenzoic acid, and the monomers containing, as a monomer of additive component, 4,4'-biphenol, hydroquinone, terephthalic acid, isophthalic acid, and/or 6-hydroxy-2-naphthoic acid, and wherein a saturated water amount of the refrigerating machine oil is 0.5% or more and 1% or less at 40 degrees Celsius and a relative humidity of 80%.