Paper strength enhancer and paper

The present invention provides a paper strength enhancer and paper, the paper strength enhancer having excellent storage stability and exhibiting a good paper strength effect when made into paper. A paper strength enhancing agent which is a mixed solution containing (A) a (meth) acrylamide polymer, (B) a water-soluble aluminum compound, (C) an inorganic acid salt (excluding the component (B) in the component (C)), and (D) an inorganic acid, the (meth) acrylamide polymer (A) contains (meth) acrylamide (a1), a polymerizable monomer (a2) having a cationic group, a polymerizable monomer (a3) having an anionic group, and a crosslinkable monomer (a4) as reaction components; when the viscosity (concentration of 15 wt%, temperature: 25 DEG C) of the prepared liquid mixture is X1 mPa.s, and the viscosity (concentration of 15 wt%, temperature: 25 DEG C) of the liquid mixture stored at 60 DEG C for 3 days is X2 mPa.s, 30 < = X1 < = 30,000 and 0.8 < = X2/X1 < = 2 are satisfied. 本发明提供一种纸力增强剂和纸，所述纸力增强剂具有优异的保存稳定性，在制成纸时表现出良好