To improve properties with respect to extrusion of a hydraulic composition and water retention properties, of an admixture for a hydraulic composition by using a water-soluble cellulose ether and a polyvinylacetamide-based compound as components of the admixture.

This admixture contains a water-soluble cellulose ether and a polyvinylacetamide-based compound, wherein as the cellulose ether, methylcellulose, hydroxyethyl cellulose, hydroxypropyl methylcellulose, hydroxyethyl methylcellulose, hydroxyethyl ethylcellulose, or the like, the 1 wt.% aqueous solution of which has an about 100-50,000 mPa.s viscosity, can be used, however, such a cellulose ether having comparatively high viscosity is desired; as the polyvinylacetamide-based compound, such a compound which has a repeating unit represented by the formula and also a weight average molecular weight of 2×104 to 2×107 and the 5 wt.% aqueous solution of which has about several tens of thousands to several hundreds of thousands mPa.s viscosity is desirably used; the blending ratio by weight of the cellulose ether to the polyvinylacetamide-based compound is desirably 5:95 to 95:5; and the admixture is added to a hydraulic composition desirably in an amount sufficient to provide a 0.2-1.5 pts.wt. ratio of the admixture to 100 pts.wt. of the total of a hydraulic material-(s) and an aggregate in the hydraulic composition. Further, the admixture can also be used for a wide variety of concrete products.