To provide a method for pretreating a papermaking raw material by which an amphoteric water-soluble polymer efficiently adsorbs on pitch particles to prevent fouling of paper caused by the pitch even when mechanical pulp or waste paper is compounded with the papermaking raw material.

The amphoteric water-soluble polymer composed of 5-95 mol% of two kinds selected from specific catonic monomers, 5-50 mol% of an anionic monomer and 0-90 mol% of a nonionic monomer is added into the papermaking raw material before papermaking to treat the papermaking raw material. A sheet of paper is then formed.