A lubricating oil composition for refrigerating machines contains a base oil and an additive in a form of a naphthalimide compound. A refrigerant used in a refrigerating machine in which the composition is used is unsaturated hydrofluorocarbon (unsaturated HFC) having a GWP of 1000 or less. When the present lubricating oil composition for refrigerating machines is used in refrigerating equipment such as an open-type automobile air-conditioner, an electric automobile air-conditioner, a gas heat pump, other air-conditioning equipment, a refrigerating machine, a vending machine, a showcase, a water-heating system and a refrigerating/heating system, it is possible to detect the leakage of a refrigerant with a long-lasting stability. Therefore, when an unsaturated freon refrigerant with a poor stability is used in the above-listed equipment, the present lubricating oil composition for refrigerating machines is significantly advantageous.