The working fluid composition for a refrigerating machine of the present invention comprises: a refrigerating machine oil comprising a mineral oil and an alkylbenzene in a mass ratio, the mineral oil/the alkylbenzene, of 85/15 to 15/85, wherein the mineral oil has a % CN by n-d-M ring analysis of 20 to 60, a pour point of −15° C. or less and a kinematic viscosity at 40° C. of 1.5 to 15 mm2/s; and a hydrocarbon refrigerant having 2 to 4 carbon atoms, wherein the refrigerating machine oil having a kinematic viscosity at 40° C. of 2 to 12 mm2/s and a flash point of 120° C. or more.