LUBRICATING OIL COMPOSITION

An object is to provide a lubricating oil composition excellent in biodegradability, rust-prevention performance, oxidation stability and lubricating property (wear resistance).The lubricating oil composition includes 100 mass parts of (A) an ester compound, 0.05 to 1.5 mass parts of (B) an amine salt of an acidic phosphoric ester and 0.01 to 0.50 mass parts of (C) a monoesterified compound.(A) Ester compound of trimethylolpropane, a straight-chain saturated fatty acid having a carbon number of 8 to 10 and adipic acid, the ester compound satisfying the relationship of TMP% : FA% : AD% of 20 to 40 % : 40 to 70 % : 5 to 25 %, respectively, provided that TMP% is assigned to a molar percentage of a component derived from trimethylolpropane, FA% is assigned to a molar percentage of a component derived from said straight-chain saturated fatty acid having a carbon number of 8 to 10, and AD% is assigned to a molar percentage of adipic acid(B) Amine salt of the acidic phosphoric ester represented by following (1) (n represents an integer of 1 or 2, R' represents an alkyl group having a carbon number of 4 to 6, and R" represents hydrogen atom or an alkyl group having a carbon number of 11 to 14.)(C) Monoesterified compound of an alkane diol having a carbon number of 3 to 8 and of succinic acid having an alkyl group having a carbon number of 8 to 18 or an alkenyl group having a carbon number of 8 to 18