The present invention is related to a shrinkage reducing agent for hydraulic materials which comprises at least one polymer selected from the group consisting of (a) a polymer having a structure derived from the residue of a compound containing 2 to 30 carbon atoms and one active hydrogen atom by the binding thereto of one oxyalkylene chain having a carboxyl-containing side chain, (b) a polymer having a structure derived from the residue of a compound containing 4 to 30 carbon atoms and two active hydrogen atoms by the binding thereto of at least one oxyalkylene chain having a carboxyl-containing side chain, (c) a polymer having a structure derived from the residue of a compound containing 1 to 30 carbon atoms and at least three active hydrogen atoms by the binding thereto of at least one oxyalkylene chain having a carboxyl-containing side chain and (d) a polymer having a structure derived from the residue of an amine by the binding thereto one oxyalkylene chain having a carboxyl-containing side chain.