The cement admixture and the cement admixture composite of the present invention can improve the water-reducing ability of cement compositions and the like and enhance the strength and durability of hardening products produced therefrom and further can adjust the viscosity of such compositions so as to facilitate the works at the sites of handling the same. The above-mentioned cement admixture is a cement admixture comprising a polycarboxylic acid polymer containing a specific site, and the above-mentioned cement admixture composite comprises two or more species of cement admixtures, wherein at least one of them is said cement admixture.