The present invention relates to a dispersant for a hydraulic composition,
containing a polymer obtained by copolymerizing a specific monomer 1 such
as an ethylenically unsaturated carboxylic acid derivative having a
polyoxyalkylene group, a monoester phosphate-based monomer 2, a diester
phosphate-based monomer 3, and an unsaturated carboxylic acid-based
monomer 4, at pH 7 or less.