Refrigerator oil, and working fluid composition for refrigerator

A working fluid composition for a refrigerating machine, comprising:

• a refrigerating machine oil;
• and
• a refrigerant comprising an unsaturated hydrofluorocarbon,
• wherein the refrigerating machine oil comprises:
• a base oil comprising a mixture of polyol esters of a saturated carboxylic acid having 4 to 10 carbon atoms and a polyhydric alcohol selected from pentaerythritol, dipentaerythritol, and a mixture thereof;
• and
• a partial ester of a carboxylic acid and pentaerythritol;
• wherein
• the carboxylic acid comprises an unsaturated carboxylic acid having 14 to 18 carbon atoms,
• the partial ester comprises a monoester of pentaerythritol, a diester of pentaerythritol, and a triester of pentaerythritol,
• the partial ester has a hydroxyl value of 20 mgKOH/g or more, and
• a content of the base oil is 90% by mass or more, and a content of the partial ester is 0.1 to 5% by mass, based on a total amount of the refrigerating machine oil.