A paper treating agent comprising 100 parts by mass of organopolysiloxane (A), from 100 to 100,000 parts by mass of water (E), and 0.1 to 100 parts by mass of a surfactant (F), characterized in that the agent further comprises 50 to 1,000 parts by mass of a cellulosic resin (C), wherein 0.5 to 2.5 hydroxyl groups per glucose unit of said cellulosic resin are etherized or esterified, and a viscosity of an aqueous 2% solution of said cellulosic resin is from 2 to 100 mPa·s.