A water-in-oil emulsion is a product form having many practical advantages. A vinylamine-based macromolecule having specific effects as papermaking chemicals and a flocculant is provided in the form of a water-in-oil emulsion having good storage stability and high performance as a flocculation treatment agent. Disclosed is a flocculation treatment agent including a water-in-oil emulsion of a water-soluble macromolecule that is produced by subjecting a water-in-oil emulsion of an aqueous poly-N-vinylcarboxylic acid amide solution coexisting with a polyoxyalkylene alkyl ether to hydrolysis in the presence of an acid or a base. Preferably, the polyoxyalkylene alkyl ether is added before the hydrolysis reaction.