Provided are an anti-wear agent comprising a heterocyclic compound having a heterocyclic skeleton derived from a compound selected from pyridines, pyrroles, pyrimidines, pyrazoles, pyridazines, imidazoles, pyrazines, triazines, triazoles, tetrazoles, oxazoles, oxadiazoles, thiazoles, thiadiazoles, furans, dioxanes, pyrans, and thiophenes and/or comprising a reaction product of the heterocyclic compound and a compound selected from a boron compound, a molybdenum compound, and a silicon compound, which is an anti-wear agent for a lubricating oil excellent in wear resistance, friction-reducing property, and base number-retaining property, and a lubricating oil composition comprising the anti-wear agent.