A method for manufacturing a powdery paper-strengthening agent including a branched (meth)acrylamide-based polymer (A) which includes a step of obtaining (A) component by polymerizing (meth)acrylamide (a1), anionic vinyl monomer (a2), cationic vinyl monomer (a3) and crosslinkable vinyl monomer (a4) in a solvent in a presence of a polymerization initiator, a step of dropping or putting the above (A) component into an organic solvent to form a precipitate, and a step of drying and pulverizing (A) component obtained as the precipitate.