To provide a polymer flocculant excellent in dehydrating effects, such as drastically improving efficiency in dehydrating sludge by forming strong and coarse flock, in treatment of sludge or waste water.

The polymer flocculant includes water-soluble polymer (A) containing vinyl group-containing monomer (a) represented by the following general formula (1) or containing (a) and (meth)acryloyl group-containing monomer (b) represented by the following general formula (2), as structural units, provided that the general formula (1) is CH₂=CH-(NR¹R²) and the general formula (2) is CH₂=CR³-CO-X-(Q-N⁺R⁴R⁵R⁶* Z^-)_m(H)_1-m.