PURPOSE: To obtain a lubricant formulation which is stable to oxidative degradation and excellent in storage stability, and can prevent the thickening of oil caused at high temperature under a frictional stress by mixing a lubricating oil with three specified additives.

CONSTITUTION: This composition is obtained by mixing a lubricating oil (A), a compound (B) of formula I (wherein X, X1 and X2 are each O, S, etc.; Rx is a 1-24C alkyl, phenyl, etc.; (a) is 1 or 2; and M+ is an alkali metal cation), an aromatic amine compound (C) selected from compounds of formulas II and III (wherein R1 is a 1-18C alkyl, naphthyl, etc.; R2 is phenyl, naphthyl, etc.; R3 is H, allyl, etc.; Ra is H, a 1-18C alkyl, etc.; and Rb and Rc are each H, a 7-9C phenylalkyl, etc.), and a compound (D) selected from (non)cyclic sterically hindered amines and phenols of formula IV (wherein R4 is H, a 5-12C cycloalkyl, etc.; R5 is a 1-24C alkyl, phenyl, etc.; and A is H, a 1-24C alkyl, etc.).