A polyoxyalkylene derivative is represented by formula (I): wherein Z represents a residue of a compound having 2 to 8 hydroxyl groups; AO represents an oxyalkylene group having 2 to 18 carbon atoms; n and m each represent an integer of 0 to 2000 provided that both n and m do not represent 0; a and b each represent an integer satisfying the relationships: 2≦a+b≦8 and 1≦b; R represents a hydrocarbon group having 1 to 30 carbon atoms; and X represents a divalent hydrocarbon group having 3 to 10 carbon atoms.