A lubricating oil composition comprising a lubricating base oil, and a mixture and/or a reaction product of (A) 0.01-0.5% by mass of at least one compound selected from among acid phosphates represented by formula (1) or formula (2), and (B) 0.01-2% by mass of an alkylamine represented by formula (3), based on the total weight of the composition, wherein the acid value due to component (A) is 0.1-1.0 mgKOH/g. [R1 and R2 represent hydrogen or straight-chain alkyl or straight-chain alkenyl groups, with at least one of R1 and R2 being a C6-12 straight-chain alkyl or straight-chain alkenyl group; R3 and R4 represent hydrogen straight-chain alkyl or straight-chain alkenyl groups, with at least one of R3 and R4 being a C13-18 straight-chain alkyl or straight-chain alkenyl group; and R5 and R6 represent hydrogen or C4-30 branched-chain alkyl groups, with at least one of R5 and R6 being a branched-chain alkyl group.]