A fluorine-containing polymer which comprises (a) a fluorine-containing (meth)acrylate monomer and (b) a nitrogen-containing monomer represented by the general formula (I): [wherein R.sup.20 represents a hydrogen atom or a group containing a sulfonic acid group, R.sup.21 represents a hydrogen atom or an alkyl group having one to four carbon atoms, and R.sup.22 represents a hydrogen atom or a methyl group]; and a treating agent composition comprising said fluorine-containing polymer. The fluorine-containing polymer and the treating agent composition can be used for imparting satisfactory water repellency and oil resistance to a sheet of paper by the use of a reduced amount thereof.