To provide a polymer having a specific parameter value with a very narrow molecular weight distribution different from the conventional copolymers despite of a polymer having a polyoxyalkylene chain, and an excellent dispersant for inorganic powders, particularly a cement addmixture. The polymer (P) in the present invention is containing a constitutional unit derived from a polyoxyalkylene chain, and satisfying a range of PD value defined as the following mathematical formula 1:1