To provide a cement admixture which can provide a cement composition markedly excellent in dispersion performance (water reduction performance) and additionally early strength developability, and can remarkably improve productivity and workability; and to provide a cement composition containing the same.

The cement admixture essentially comprises a polycarboxylic acid-based copolymer and an organic curing accelerator, wherein the polycarboxylic acid-based copolymer comprises a structural unit (A) originated from an unsaturated polyalkylene glycol ether-based monomer (a) represented by formula (1): YO(R1O)nR2, and a structural unit (B) originated from an unsaturated carboxylic acid-based monomer (b).