A lubricant additive includes a monoester carboxylic acid salt (A) represented by formula (1). In formula (1), R1 represents a single bond between carbon atoms of carbonyl groups, or a divalent hydrocarbon group having 1 to 4 carbon atoms, and R2 represents a hydrocarbon group having 1 to 22 carbon atoms. AO represents an oxyalkylene group of one type selected from oxyalkylene groups having 2 to 4 carbon atoms, or a mixed oxyalkylene group of two or more types selected from oxyalkylene groups having 2 to 4 carbon atoms, and n is an average number of added moles of the oxyalkylene group represented by AO and is 0 to 5. M represents organic ammonium.