The first lubricating oil composition of the present invention is a composition comprising a polycarbonate represented by the following general formula, at least one compound as an essential component selected from the group consisting of epoxy compounds, phenol compounds, sulfur compounds and amine compounds, and a triester phosphite compound and a triester phosphate compound as an optical component. R<5>OCOOÄ(R<6>O)pCOOÜnR<7> wherein R<5> and R<7> are each independently a specific hydrocarbon group or a specific hydrocarbon group containing an ether bond, R<6> is a specific alkylene group, and p and n are specific integers. The lubricating oil compositions are excellent in lubricating properties, cleaning properties and electrical insulating properties, and their viscosity at low temperature can readily be lowered and, in addition thereto, generation of carbon dioxide gas can be inhibited.