Refrigerating machine oil, and working fluid composition for refrigerating machines

A refrigerating machine oil comprising:

• a base oil comprising a polyol ester obtainable by synthesis from
• a polyhydric alcohol comprising pentaerythritol and
• a fatty acid comprising isobutanoic acid and 3,5,5-trimethylhexanoic acid;
• a sulfide compound comprising at least one selected from the group consisting of diphenyl sulfide, dibenzyl sulfide, didecyl sulfide, didodecyl sulfide and thiobisphenol compounds;
• and
• an orthophosphoric acid ester comprising at least one selected from the group consisting of triphenyl phosphate, tricresyl phosphate, and an alkylphenyl phosphate having a C3-C4 alkyl group,
• wherein
• a content of the sulfide compound is 0.1 to 0.5% by mass and
• a content of the orthophosphoric acid ester is 0.2 to 2.0% by mass, based on a total amount of the refrigerating machine oil, and
• the refrigerating machine oil having a kinematic viscosity at 40° C. of 5 to 150 mm2/s.