PROBLEM TO BE SOLVED: To provide a friction reducing agent capable of significantly reducing frictional resistance of an aqueous liquid, a coating material containing the friction reducing agent, and a friction reducing method using the friction reducing agent.SOLUTION: The friction reducing agent comprises a water-soluble polymer compound having an ammonium salt structure in a side chain. The water-soluble polymer compound preferably has a repeating unit represented by formula (1) or (2). (Ris H or a methyl group; A is O or an NH group; Ris an alkylene group or an arylene group; Rto Rare each independently an alkyl group or an aryl group; and Xand Xare each a monovalent anion.)SELECTED DRAWING: None
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