Lubricating oil composition containing cyclic organophosphorus compound

A lubricating oil composition which comprises a base oil and at least one compound selected from cyclic organic phosphorus compounds represented by following general formula (I):

• 29
• wherein Z represents hydrogen atom, an alkyl group, a cycloalkyl group which may be substituted with alkyl groups having 1 to 12 carbon atoms and/or hydroxyl group, an aryl group which may be substituted with alkyl groups having 1 to 12 carbon atoms and/or hydroxyl group or an alkyl group substituted with an aryl group which may be substituted with at least one of alkyl groups having 1 to 12 carbon atoms and hydroxyl group, X1 and X2 each independently represent a halogen atom or hydroxyl group and p and q each represent an integer of 0 to 3.