There is obtained a lubricating oil having good solubility with both HFC refrigerant and contaminants by adding PAG having a viscosity of not more than 70cSt (40 DEG C) to a synthetic lubricating oil, such as polyvinyl ether and ester oils at an amount of not less than 0.1wt% and not more than 20wt% (desirably, not less than 2wt% and not more than 10wt%). Therefore, in a refrigerating/air-conditioning machine equipped with a compressor using this present lubricating oil together with a HFC refrigerant as a working fluid, deflection in the ratio of the mixture within the machines is not caused and, consequently, the efficiency for washing capillary tubes is not reduced. In that case, a high-reliable refrigerating/air-conditioning machine can be obtained at a low price without any modification of the refrigerating/air-conditioning machine.