To obtain an abrasion resistance improver which has excellent extreme pressure properties equivalent to or higher than those of chlorinated paraffin, though it does not contain chlorine atom, and is excellent in compatibility with a base oil (e.g. a mineral oil) by compounding a phosphoric-ester-group- containing polyether compound with an amine compound.

This abrasion resistance improver is prepared by compounding (A) at least one phosphoric-ester-group-containing polyether compound selected from among compounds represented by formulas I, II, and III with (B) at least one amine compound selected from among compounds represented by formulas IV and V in a wt. ratio of A/B of (5/1)-(1/5). In the formulas, R1 is a 1-30C monovalent hydrocarbon group; R2 is a 1-20C divalent hydrocarbon group; A1O is 3-4C oxyalkylene; p is 18-100; q is 0 or 1-40; s is 10-50; t is 0 or 1-20; R3 is 8-22C alkyl or alkenyl; R4 and R5 are each 4-22C alkyl or alkenyl; A2O is oxypropylene; m and n are each 1-19 provided m+n is 2-20; and r is 1-20.