The present invention relates to a cement dispersant, and an object thereof is to provide a cement dispersant having high water reducing property, low setting retardation and low concrete viscosity and taking also applicability into account. The cement dispersant comprises a polycarboxylic acid polymer formed by structural unit (I) composed of a reactive alcohol alkylene oxide adduct and structural unit (II) composed of a reactive dibasic acid, and preferably further structural unit (III) containing polyamide polyamine in the unit, wherein fumaric acid and/or a derivative thereof is used as a partial or main starting material of the structural unit (II). The cement dispersant is excellent in water reducing property, setting retardation and concrete viscosity.