To provide an admixture using a slump loss preventing agent giving excellent slump loss preventing ability and giving excellent shrinkage reducing ability and compressive strength to a hardened body even using moderate heat portland cement and concrete using the admixture.

A carboxylic acid monoester copolymer obtained by radical-polymerizing a mixture containing ≥90 mol% in total of respective following monomers in a molar ratio of 75/25-45/55 under a prescribed condition and having mass average molecular weight of 2,000-60,000 is used. A carboxylic acid monoester expressed by formula (1) and an allyl alcohol-based compound expressed by formula (2) are used. In the formulas (1) and (2), R represents a 4C or 5C alkyl group, (n) represent integers of 2-4 and A represents a residue obtained by removing all hydroxy groups from a polyalkylene glycol having a polyoxyalkylene group comprising 2-150 oxyethylene units only or 2-150 in total of oxyethylene units and oxypropylene units.

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