Refrigerator oil and working fluid composition for refrigerator

In an aspect, the present invention provides a refrigerating machine oil comprising a poly(meth)acrylate as a base oil, wherein the poly(meth)acrylate comprises a hydrogenated poly(meth)acrylate, a content of a unit having a carbon-carbon double bond present at a terminal in the poly(meth)acrylate is 6% by mole or less relative to total units constituting the poly(meth)acrylate, and a kinematic viscosity at 40° C. of the hydrogenated poly(meth)acrylate is 1 to 1000 mm2/s, the refrigerating machine oil being used with a refrigerant comprising a refrigerant selected from 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, an unsaturated hydrofluorocarbon, a hydrocarbon, and carbon dioxide.