The present invention is thus directed to a cement additive which comprises a copolymer (A) obtained by polymerizing a monomer mixture (K), wherein; said monomer mixture (K) comprises a polyalkylene glycol ester monomer (I) represented by the general formula (1): <CHEM> a polyalkylene glycol ester monomer (II) represented by the general formula (2): <CHEM> and a carboxylic acid monomer (III) represented by the general formula (3). <CHEM>
