PURPOSE: To produce the titled polymer, by extruding an aqueous solution prepared by adding a water-soluble alcohol and a water-soluble inorganic alkaline earth metal salt to an aqueous solution containing a specified polymer through an orifice into a low-temperature, water-soluble alcohol.

CONSTITUTION: The titled polymer is produced by extruding a uniformly extrudable solution obtained by dissolving a water-soluble alcohol and a water-soluble inorganic alkaline earth metal salt in an aqueous solution containing an acrylic acid hydrazide polymer represented by the formula, wherein X is H or CH 3, A is a monomer unit selected from the group consisting of (meth) acrylamide, (meth) acrylate esters or their hydrolyzate (inorganic salts), B is a monomer unit other than A, copolymerizable with (meth) acrylamide or (meth) acrylate ester and l, m and n are numbers satisfying the relationships: 0mol%<l≤100mol% and l+m+n=100mol%, through an orifice into a water-soluble alcohol at a temperature below its solidification point, thereby forming a solid product and separating and drying the product. This product is useful as a coagulant, a heavy metal-adsorbing agent or the like.