The present invention provides a refrigerating machine oil comprising, as a base oil, a polymer having a structural unit represented by the following formula (1): wherein R 1 , R 2 and R 3 , which may be the same as or different from each other, represent a hydrogen atom or a hydrocarbon group; and R 4 represents a hydrocarbon group or an organic group containing an oxygen atom, and having a number average molecular weight Mn of 300 or more and 3000 or less and a ratio of a weight-average molecular weight Mw to a number average molecular weight Mn (Mw/Mn) of 1.10 or more and 2.00 or less, and the refrigerating machine oil being used with a refrigerant selected from the group consisting of difluoromethane, a mixture of difluoromethane and pentafluoroethane, a mixture of difluoromethane, pentafluoroethane and 1,1,1,2-tetrafluoroethane, a mixture of pentafluoroethane, 1,1,1,2-tetrafluoroethane and 1,1,1-trifluoroethane, unsaturated hydrofluorocarbons, hydrocarbons and carbon dioxide.