The hydrophilic dispersion polymer comprises (a) a cationic monomer represented by the following general formula (I): ##STR1## wherein R1 is H or CH3; each of R2 and R3 is an alkyl group having 1 to 2 carbon atoms; R4 is H or an alkyl group of 1 to 2 carbon atoms; A' is an oxygen atom or NH; B' is an alkylene group of 2 to 4 carbon atoms or a hydroxypropylene group; and X- is an anionic counterion