Refrigerating machine oil

A refrigerating machine oil comprising:

• a lubricating base oil comprising a mineral oil;
• a phosphorus-containing additive comprising at least one selected from the group consisting of triphenyl phosphate, tricresyl phosphate and triphenyl phosphorothionate;
• and
• a polymer selected from the group consisting of:
• (I) a copolymer comprising at least one of a first (meth)acrylic acid ester and at least one of a second (meth)acrylic acid ester, as monomer units, the first (meth)acrylic acid ester having a linear alkyl group having 1 to 18 carbon atoms, and the second (meth)acrylic acid ester having a 2-position branched alkyl group having 4 or more and less than 20 carbon atoms, wherein the copolymer of (I) is selected from:
• (i) a copolymer consisting of the first (meth)acrylic acid alkyl ester and the second (meth)acrylic acid alkyl ester, as monomer units, and
• (ii) a copolymer consisting of the first (meth)acrylic acid alkyl ester, the second (meth)acrylic acid alkyl ester and an α-olefin having 8 to 12 carbon atoms, as monomer units;
• and
• (II) a copolymer consisting of a maleic acid ester and an α-olefin having 8 to 12 carbon atoms, as monomer units, wherein the maleic acid ester is an ester of maleic acid and an alcohol comprising a linear aliphatic alcohol having 4 to 10 carbon atoms,
• wherein the polymer has a number average molecular weight (Mn) of 4000 or more and 20000 or less, a weight average molecular weight (Mw) of 8000 or more and 30000 or less, and an Mw/Mn of 1.2 or more and 2.5 or less,
• wherein the refrigerating machine oil has a kinematic viscosity at 40° C. of 10 mm2/s or less, and is used with a refrigerant, and
• wherein
• a content of the lubricating base oil is 90% by mass or more,
• a content of the phosphorus-containing additive is 0.1% by mass or more and 3% by mass or less, and
• a content of the polymer is 0.5% by mass or more and 5% by mass or less, based on the total amount of the refrigerating machine oil.