To enable a remarkable improvement in filler yield by adding a specific cationic polymer microparticle to a stock in the neutral papermaking.

The cationic polymer microparticle for addition to a stock is obtained by carrying out the emulsion copolymerization of 70-95 wt.% ethylenically unsaturated monomer represented by the formula (R1 is H or CH3; R2 is phenyl or acetoxyl), e.g. styrene with 0-30 wt.% cationic monomer such as methacrylamidopropyltrimethylammonium chloride and 1-2 wt.% cationic surfactant such as cetylmethyltrimethylammonium bromide using 0.5-5 wt.% cationic polymerization initiator such as 2,2-azobis(N,N'-dimethylene- isobutylamine)dihydrochloride. The resultant microparticle has cationic properties at pH ≤11 and ≤100 nm particle diameter. The microparticle in an amount of 0.04-2.0 wt.% based on the bone-dry solid content of the stock is added thereto and a water-soluble anionic acrylamide having ≥1000,000 molecular weight is then added thereto.