PURPOSE: To obtain the titled compsn. having a high traction coefficient as well as excellent oxidation stability, abrasion resistance and flaking resistance, by incorporating a compd. such as phosphate, phosphite or molybdenum thiocarbamate with a base oil comprising a particular hydrocarbon compd.

CONSTITUTION: A base oil comprising a hydrocarbon compd. of the formula [wherein R1WR3 are each independently a 1W4C alkyl; R4WR5 are each independently (1W4C alkylene-substd.) methylene, ethylene or trimethylene; aWc are each independently an integer of 0W2; and x is an integer of 0 or 1] (e.g.: 2,4- dicyclohexyl-2-melthylpentane) is blended with 0.1W10wt.% (based on the total weight of the compsn.) at least one compd. selected from among phosphate, phosphite, phosphoroamidate, amine phosphate, molybdenum dithiophosphate, and molybdenum dithiocarbamate and, if necessary, an antioxidant, a viscosity index improve, a corrosion inhibitor, a rust preventive etc.