The purpose of the present invention is to provide an extreme pressure agent which does not contain any metal element or the like and is highly safe but which exhibits performance equivalent to those of conventional extreme pressure agents each containing a metal element or the like when used in lubrication purposes. This extreme pressure agent comprises a copolymer (A) which comprises an alkyl acrylate (a) represented by general formula (1) and a hydroxyalkyl acrylate (b) represented by general formula (2) as the essential constituent monomers, and is characterized in that the reaction ratio of the component (a) to the component (b) (i.e., (a)/(b)) is 50/50 to 80/20 (by mole) and the copolymer (A) has a weight average molecular weight of 40,000-150,000. (In formula (1), R1 represents an alkyl group having 10-18 carbon atoms.) (In formula (2), R2 represents an alkylene group having 2-4 carbon atoms.) (in the formula, R 1 represents an alkyl group having 10 to 18 carbon atoms) (in the formula, R 2 represents an alkylene group having 2 to 4 carbon atoms).