Use of a refrigerating machine oil with a refrigerant comprising trifluoroiodomethane, the refrigerating machine oil comprising: 50% by mass or more based on a total amount of the refrigerating machine oil of an ester-based base oil that is at least one selected from the group consisting of a polyol ester and a complex ester, wherein the polyol ester is an ester of a polyhydric alcohol and a fatty acid having 4 to 9 carbon atoms; at least one epoxy compound selected from the group consisting of an alkyl glycidyl ether and an aryl glycidyl ether; and a phenol-based antioxidant, wherein a content of the epoxy compound is 0.7% by mass or more based on a total amount of the refrigerating machine oil, with the proviso that the use of a refrigerating machine oil with a refrigerant that is a mixture of difluoromethane, trifluoroiodomethane (CF 3 I) and 1,1,1,2,2-pentafluoroethane at a mass ratio of 50.0: 38.0: 12.0, wherein the refrigerating machine oil consists of: 95.70% by mass of an ester of pentaerythritol with a mixture of octanoic acid (C8 acid) and nonanoic acid (C9 acid) (C8 acid/C9 acid = 1/1.1 (molar ratio)) having a hydroxyl number of 1.0 (mgKOH/g), a 100°C kinematic viscosity of 8.5 (mm 2 /s) and a number- average molecular weight (Mn) of 670; 0.3% by mass of 2,6-di-tert-butyl-4-methylphenol; 3.0% by mass of 2-ethylhexyl glycidyl ether; and 1.0% by mass of tricresyl phosphate and a silicone antifoaming agent, based on a total amount of the refrigerating machine oil; wherein the weight ratio of the refrigerant and the refrigerating machine oil is 1:1; is excluded. 50% by mass or more based on a total amount of the refrigerating machine oil of an ester-based base oil that is at least one selected from the group consisting of a polyol ester and a complex ester, wherein the polyol ester is an ester of a polyhydric alcohol and a fatty acid having 4 to 9 carbon atoms; at least one epoxy compound selected from the group consisting of an alkyl glycidyl ether and an aryl glycidyl ether; and a phenol-based antioxidant, wherein a content of the epoxy compound is 0.7% by mass or more based on a total amount of the refrigerating machine oil, with the proviso that the use of a refrigerating machine oil with a refrigerant that is a mixture of difluoromethane, trifluoroiodomethane (CF 3 I) and 1,1,1,2,2-pentafluoroethane at a mass ratio of 50.0: 38.0: 12.0, wherein the refrigerating machine oil consists of: 95.70% by mass of an ester of pentaerythritol with a mixture of octanoic acid (C8 acid) and nonanoic acid (C9 acid) (C8 acid/C9 acid = 1/1.1 (molar ratio)) having a hydroxyl number of 1.0 (mgKOH/g), a 100°C kinematic viscosity of 8.5 (mm 2 /s) and a number- average molecular weight (Mn) of 670; 0.3% by mass of 2,6-di-tert-butyl-4-methylphenol; 3.0% by mass of 2-ethylhexyl glycidyl ether; and 1.0% by mass of tricresyl phosphate and a silicone antifoaming agent, based on a total amount of the refrigerating machine oil; wherein the weight ratio of the refrigerant and the refrigerating machine oil is 1:1; 95.70% by mass of an ester of pentaerythritol with a mixture of octanoic acid (C8 acid) and nonanoic acid (C9 acid) (C8 acid/C9 acid = 1/1.1 (molar ratio)) having a hydroxyl number of 1.0 (mgKOH/g), a 100°C kinematic viscosity of 8.5 (mm 2 /s) and a number- average molecular weight (Mn) of 670; 0.3% by mass of 2,6-di-tert-butyl-4-methylphenol; 3.0% by mass of 2-ethylhexyl glycidyl ether; and 1.0% by mass of tricresyl phosphate and a silicone antifoaming agent, based on a total amount of the refrigerating machine oil; wherein the weight ratio of the refrigerant and the refrigerating machine oil is 1:1; is excluded.